Yellow squiggly lines begone!
Done automatically on .cpp files through `run-clang-tidy`, with manual corrections to the mistakes.
If an import is directly used, but is technically unnecessary since it's recursively imported by something else, it is *not* removed.
The tool doesn't touch .h files, so I did some of them by hand while fixing errors due to old recursive imports.
Not everything is removed, but the cleanup should be substantial enough.
Because this done on Linux, code that isn't used on it is mostly untouched.
(Hopefully no open PR is depending on these imports...)

Core::GetState reads from four different pieces of state: s_is_stopping,
s_hardware_initialized, s_is_booting, and CPUManager::IsStepping.
I'm keeping that last one as is for now because there's code in Dolphin
that sets it directly, but we can unify the other three to make things
easier to reason about.

This commit also gets rid of s_is_started. This was previously used in
Core::IsRunningAndStarted to ensure true wouldn't be returned until the
CPU thread was started, but it wasn't used in Core::GetState, so
Core::GetState would happily return State::Running after we had
initialized the hardware but before we had initialized the CPU thread.
As far as I know, there are no callers that have any real need to know
whether the boot process is currently initializing the hardware or the
CPU thread. Perhaps once upon a time there was a desire to make the
apploader debuggable, but a long time has passed without anyone stepping
up to implement it, and the way CBoot::RunApploader is implemented makes
it rather difficult. So this commit makes all the functions in Core.cpp
consider the core to still be starting until the CPU thread is started.

On Windows 11, when playing windowed in a separate window/widget from the main emulator window, we don't want the window to have rounded corners, as it prevents the corner pixels from being visible

Co-authored-by: Admiral H. Curtiss <pikachu025@gmail.com>