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...)

cpp-ipc is explicitely only available on Windows, Linux, QNX, and FreeBSD. Trying to build dolphin on any another BSD such as OpenBSD or Haiku currently leads to failure because of this.

Since v1.4.0, cpp-ipc now supports FreeBSD. This was a limitation that
prevented us from enabling compilation on FreeBSD in #13870.

Full changelog: https://github.com/mutouyun/cpp-ipc/releases/tag/v1.4.0

Core/HW: Add Broadband Adapter (IPC).

This is a hassle-free BBA option intended for local play with multiple
Dolphin instances running *in the same system*. After selecting
**Broadband Adapter (IPC)** in the **SP1** slot in the GameCube section
in the settings, games that support LAN play will be able to discover
each other, without requiring third-party software or relatively complex
TAP setups.

The implementation is based on cpp-ipc, a high-performance inter-process
communication library that uses shared memory as transport layer.

Supported platforms are:

- [x] Linux
- [x] Windows
- [ ] macOS (cpp-ipc does not support this platform)
- [ ] FreeBSD (cpp-ipc does not support this platform)
- [ ] Android (cpp-ipc needs some adjustments; while it could work,
  launching two Dolphin instances within the same Android system may be
  both challenging and impractical)