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...)

The core no longer cares which thread is the host thread.

Cleaning up Android's HostThreadLock is left for another PR, in part
because the HostThreadLock in NativeConfig.cpp still serves a purpose,
and in part to make any issues easier to bisect.

The `QtUtils::AdjustSizeWithinScreen()` function now centers the
widget on their parent window after the widget's size is adjusted. This
is required in some desktop environments (generally on Linux systems) to
ensure that the just-resized widget remains aligned with its parent
window.

The creation of the **Cheats Manager** dialog is now deferred to first
show, as creating it within the main window's constructor prevents the
dialog from knowing the real position of its parent window, which is
only properly calculated on first show.

For the same reasons, the analytics prompt is now shown only when the
application is ready (i.e. when the main window has been shown).

| Before | After |
| ------ | ----- |
| <img width="1920" height="1080" alt="[Dolphin Emulator] Misplaced analytics prompt" title="[Dolphin Emulator] Misplaced analytics prompt" src="https://github.com/user-attachments/assets/c3e43b3b-cf79-4398-b531-7de6068c583e" /> | <img width="1920" height="1080" alt="[Dolphin Emulator] Centered analytics prompt" title="[Dolphin Emulator] Centered analytics prompt" src="https://github.com/user-attachments/assets/a10d06d9-7438-4032-b96c-dfcb48826349" /> |
| <img width="1920" height="1080" alt="[Dolphin Emulator] Misplaced Settings dialog" title="[Dolphin Emulator] Misplaced Settings dialog" src="https://github.com/user-attachments/assets/f35b10ee-4f07-48d4-86f9-2537ad5ca7ca" /> | <img width="1920" height="1080" alt="[Dolphin Emulator] Centered Settings dialog" title="[Dolphin Emulator] Centered Settings dialog" src="https://github.com/user-attachments/assets/33e37237-77a4-44f6-a0e2-b709f65b672b" /> |
| <img width="1920" height="1080" alt="[Dolphin Emulator] Misplaced Cheats Manager dialog" title="[Dolphin Emulator] Misplaced Cheats Manager dialog" src="https://github.com/user-attachments/assets/1fbd3836-5639-4d5a-b57e-e2e21f21c9db" /> | <img width="1920" height="1080" alt="[Dolphin Emulator] Centered Cheats Manager dialog" title="[Dolphin Emulator] Centered Cheats Manager dialog" src="https://github.com/user-attachments/assets/3f2b1b50-de16-49b7-bac4-c444c6cab0bc" /> |

In certain cases, the platform can be "wayland-egl", "wayland-xcomposite", and other values for which I haven't found a full list yet. Instead of matching only "wayland", we now look for "wayland" anywhere in the `QT_QPA_PLATFORM` string in a case-insensitive manner.

Acknowledgements:
`CaseInsensitiveContains`' implementation was heavily inspired by GNU's non-standard glibc `strcasestr` function, which can be found here licensed under GPLv2 or later: https://ftp.gnu.org/gnu/libc/

Dolphin already uses QStyleHints::colorScheme to detect dark mode,
so this code is now redundant.

bugfix:  SetQWidgetWindowDecorations(this); not called before show() for Windows darkmode titlebars.

The actual call to (QWidget) show() needed to come sooner. Show() was originally left alone, but with other checks needing to move with (QWidget) show(), this function became less useful.  Show()  was originally created to fix the render widget appearing behind the main window, but that appears to work fine in this iteration.