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...)
Recently came across a strange issue where Dolphin would hard crash in most games with this error:
```sh
/usr/include/c++/15.2.1/optional:1165: constexpr const _Tp* std::optional<_Tp>::operator->() const [with _Tp = InputCommon::ImagePixelData]: Assertion 'this->_M_is_engaged()' failed.
```
The culprit turned out to be accessing `host_key_image` which is an `std::optional` thay may return `std::nullopt`. I'm not sure why this issue started occuring for me since I've had no issue with my Dynamic Input Textures in the past? But this fixes a crash if the image fails to load.
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.
