When using clang and libstdc++, compiling fails with these errors:

```
FAILED: [code=1] Source/Core/VideoCommon/CMakeFiles/videocommon.dir/PerformanceMetrics.cpp.o
/usr/sbin/ccache /usr/sbin/clang++ -DAUTOUPDATE=1 -DDATA_DIR=\"/usr/local/share/dolphin-emu/\" -DHAS_OPENGL -DHAS_VULKAN -DHAVE_CPPIPC -DHAVE_LIBSYSTEMD -DIMGUI_USER_CONFIG=\"imgui_user_config.h\" -DLZMA_API_STATIC -DOFF -DPUGIXML_NO_EXCEPTIONS -DRC_CLIENT_SUPPORTS_HASH -DSFML_STATIC -DSPNG_STATIC -DTINYGLTF_NOEXCEPTION -DTINYGLTF_NO_EXTERNAL_IMAGE -DTINYGLTF_USE_CPP14 -DUSE_ANALYTICS=1 -DUSE_MEMORYWATCHER=1 -DUSE_PIPES=1 -DUSE_RETRO_ACHIEVEMENTS -DZSTD_MULTITHREAD -D_ARCH_64=1 -D_DEFAULT_SOURCE -D_FILE_OFFSET_BITS=64 -D_LARGEFILE_SOURCE -D_M_X86_64=1 -D__LIBUSB__ -D__STDC_CONSTANT_MACROS -D__STDC_LIMIT_MACROS -I/dolphin-local/Source/Core -I/dolphin-local/Externals/picojson -I/dolphin-local/build/release/x64/Source/Core -I/dolphin-local/Externals/enet/enet/include -I/dolphin-local/Externals/fmt/fmt/include -I/dolphin-local/Externals/mbedtls/include -I/dolphin-local/Externals/minizip-ng/minizip-ng -I/dolphin-local/Externals/liblzma/api -I/dolphin-local/Externals/zstd/zstd/build/cmake/../../lib -I/dolphin-local/Externals/libiconv/include -I/dolphin-local/build/release/x64/Externals/libiconv/lib -I/dolphin-local/Externals/libiconv/libcharset/include -I/dolphin-local/build/release/x64/Externals/libiconv/libcharset -I/dolphin-local/Externals/SFML/SFML/include -I/dolphin-local/Externals/bzip2/bzip2 -I/dolphin-local/Externals/expr/include -I/dolphin-local/Externals/hidapi/hidapi-src/hidapi -I/dolphin-local/Externals/pugixml/pugixml/src -I/dolphin-local/Externals/glslang/glslang/glslang/.. -I/dolphin-local/build/release/x64/include -I/dolphin-local/Externals/rcheevos -I/dolphin-local/Externals/libspng/libspng/spng -I/dolphin-local/Externals/xxhash/xxHash -I/dolphin-local/Externals/imgui -I/dolphin-local/Externals/imgui/imgui -I/dolphin-local/Externals/implot/implot -I/dolphin-local/Externals/glslang/glslang/SPIRV/.. -I/dolphin-local/Externals/tinygltf -isystem /dolphin-local/Externals/libusb/libusb/libusb -isystem /dolphin-local/Externals/glslang/glslang -isystem /dolphin-local/Externals/glslang/glslang/Public -isystem /dolphin-local/Externals/glslang -Qunused-arguments -fcolor-diagnostics -O3 -DNDEBUG -std=c++23 -msse2 -fdiagnostics-color -fno-strict-aliasing -fno-exceptions -fvisibility-inlines-hidden -fvisibility=hidden -fomit-frame-pointer -Wall -Wtype-limits -Wsign-compare -Wignored-qualifiers -Wuninitialized -Wshadow -Wshadow-field-in-constructor -Winit-self -Wmissing-declarations-Wmissing-variable-declarations -Werror=format -Wno-trigraphs -MD -MT Source/Core/VideoCommon/CMakeFiles/videocommon.dir/PerformanceMetrics.cpp.o -MF Source/Core/VideoCommon/CMakeFiles/videocommon.dir/PerformanceMetrics.cpp.o.d -o Source/Core/VideoCommon/CMakeFiles/videocommon.dir/PerformanceMetrics.cpp.o -c /dolphin-local/Source/Core/VideoCommon/PerformanceMetrics.cpp
In file included from /dolphin-local/Source/Core/VideoCommon/PerformanceMetrics.cpp:4:
/dolphin-local/Source/Core/VideoCommon/PerformanceMetrics.h:69:51: error: no matching constructor for initialization of 'std::atomic<FrameBufferSize>'
   69 |   std::atomic<FrameBufferSize> m_frame_buffer_size{};
      |                                                   ^~
/usr/bin/../lib64/gcc/x86_64-pc-linux-gnu/16/../../../../include/c++/16/atomic:237:17: note: candidate constructor not viable: constraints not satisfied
  237 |       constexpr atomic() noexcept(is_nothrow_default_constructible_v<_Tp>)
      |                 ^
/usr/bin/../lib64/gcc/x86_64-pc-linux-gnu/16/../../../../include/c++/16/atomic:238:11: note: because 'is_default_constructible_v<PerformanceMetrics::FrameBufferSize>' evaluated to false
  238 |         requires is_default_constructible_v<_Tp>
      |                  ^
/usr/bin/../lib64/gcc/x86_64-pc-linux-gnu/16/../../../../include/c++/16/atomic:246:7: note: candidate constructor not viable: requires 1 argument, but 0 were provided
  246 |       atomic(const atomic&) = delete;
      |       ^      ~~~~~~~~~~~~~
/usr/bin/../lib64/gcc/x86_64-pc-linux-gnu/16/../../../../include/c++/16/atomic:252:17: note: candidate constructor not viable: requires single argument '__i', but no arguments were provided
  252 |       constexpr atomic(_Tp __i) noexcept : _M_i(__i)
      |                 ^      ~~~~~~~
1 error generated.
```

This was tested and occurs on both Arch and Alpine Linux.

fb4ff3e added a statistics option to show the internal resolution, but
it just showed the total size of the EFB (which is always 640x528) times
the IR scale, so it didn't convey any useful information.

This commit instead makes the option use the size of the last XFB copy
(not multiplied by the IR scale), which changes based on the game's
rendering resolution.

This avoids the static initialization order fiasco between Core and VideoCommon

Co-authored-by: Jordan Woyak <jordan.woyak@gmail.com>

Use the normal state changed `HookableEvent` instead of having
`Core::NotifyStateChanged` call `g_perf_metrics.OnEmulationStateChanged`
directly.

The direct call was added in bad78cfed416d89ceb6b0acf6c134d3691b3d624 to
avoid a crash. At the time state changed callbacks were stored in a
vector, and the crash was caused by `g_perf_metric`'s destructor trying
to remove the callback from the already-destroyed vector.

Later a97627e736ff352e031123519c799e65cc98b32c switched state changed
callbacks to use `HookableEvent`, which is specifically designed to
handle the case where a hook outlives its associated event.

Since the workaround is no longer necessary replace it with a standard
`EventHook`.

Previously, PerformanceTracker registered a callback to be updated on
emulation state changes. PerformanceTrackers live in a global variable
(g_perf_metrics) within libvideocommon. The callback was stored in a
global variable in libcore. This created a race condition at shutdown
between these libraries, when the PerfTracker's destructor tried to
unregister the callback.
Notify the PerfTracker directly from libcore, without callbacks, since
Core.cpp already references g_perf_metrics explicitly. Also rename
Core::CallOnStateChangedCallbacks to NotifyStateChanged to better
reflect what it's doing.

PerformanceTracker: Eliminate mutex. General cleanups.