Core: Add SDL Hints settings

Signed-off-by: Andrew Strauss <astrauss11@gmail.com>

Previously, when an input device was connected or disconnected, we would
recreate all devices. This commit makes it so we only touch the relevant
device instead. This matters because recreating a device causes us to
drop all held buttons for that device. Due to Android only delivering
inputs as events, we're unable to poll for currently held buttons when
recreating a device.

This recently became a problem for users of Ayn devices due to a
firmware update. Every now and then, something about the display
viewports changes, triggering an update to an input device that I assume
is a touch input device. This input device isn't something users
normally map in Dolphin's controller settings, but it changing was
causing Dolphin to drop all held buttons for the device's built-in
gamepad as well as any other connected gamepads.

Remove unused vector `controller_names` from `LoadConfig` and
`SaveConfig`. The vector has names added to it but they're never used.

Prior to d03f9032c129e440e4f07d319be8b52500798e07 these vectors were
passed to `DynamicInputTextureManager::GenerateTextures`, but that
commit removed those calls.

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...)