Accomplished using `run-clang-tidy` with `performance-move-const-arg,performance-unnecessary-value-param,modernize-pass-by-value`.

Changed arguments to const references, removed them where inappropriate (e.g. sink parameters). Same with std::move.

Manually reviewed each change to make sure that it makes sense, and do something more appropriate if possible.

The status bar shows the number of games in your collection. If any
games are hidden by the platform, region, or search filters it will also
show how many games are visible and how many are filtered.

The visibility of the status bar can be toggled from the menu by
selecting `View`->`Show Game Count`.

Implements https://bugs.dolphin-emu.org/issues/9517.

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...)

Since Grid View doesn't have a header for users to change sorting
options with, use List View's sorting in Grid View too.

Fix some common anti-patterns with these data structures.

- You can dereference the iterator returned by `find` to access the
  underlying value directly, without an extra `operator[]`/`at`.
- Rather than checking for an element before insertion/deletion, you can
  just do the operation and if needed check the return value to
  determine if the insertion/deletion succeeded.

Emit the dataChanged signal when adding or removing tags from a game.
This both updates the contents of the game's Tags column immediately
(instead of having to wait for the context menu to be closed), and
updates the sorting if games are being sorted by the Tags column.

Use NonAutodismissibleMenu for MenuBar's Options, JIT, and
Tools->"Connect Wii Remotes" menus, as well as for the Tags menu in
GameList's context menu.

NonAutodismissibleMenu allows users to check or uncheck multiple
checkable menu items without closing the menu between selections.