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...)

SPDX standardizes how source code conveys its copyright and licensing
information. See https://spdx.github.io/spdx-spec/1-rationale/ . SPDX
tags are adopted in many large projects, including things like the Linux
kernel.

Noticed missing include as a build failure on gcc-11:

```
[ 26%] Building CXX object Source/Core/DiscIO/CMakeFiles/discio.dir/WIACompression.cpp.o
../../../../Source/Core/DiscIO/WIACompression.cpp: In lambda function:
../../../../Source/Core/DiscIO/WIACompression.cpp:170:31: error: 'numeric_limits' is not a member of 'std'
  170 |         std::min<size_t>(std::numeric_limits<unsigned int>().max(), x));
      |                               ^~~~~~~~~~~~~~
../../../../Source/Core/DiscIO/WIACompression.cpp:170:46: error: expected primary-expression before 'unsigned'
  170 |         std::min<size_t>(std::numeric_limits<unsigned int>().max(), x));
      |                                              ^~~~~~~~
```

Signed-off-by: Sergei Trofimovich <slyfox@gentoo.org>

By calling ZSTD_CCtx_setPledgedSrcSize, we can let zstd know
how large a chunk is going to be before which start compressing
it, which lets zstd avoid allocating more memory than needed
for various internal buffers. This greatly reduces the RAM usage
when using a high compression level with a small chunk size,
and doesn't have much of an effect in other circumstances.

A side effect of calling ZSTD_CCtx_setPledgedSrcSize is that
zstd by default will write the uncompressed size into the
compressed data stream as metadata. In order to save space,
and since the decompressed size can be figured out through
the structure of the RVZ format anyway, we disable writing
the uncompressed size by setting ZSTD_c_contentSizeFlag to 0.

This could cause read errors if chunks were laid out a certain
way in the file and the whole chunk wasn't being read at once.
Should fix https://bugs.dolphin-emu.org/issues/12184.