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.

Co-authored-by: Dentomologist <dentomologist@gmail.com>

The callback mechanism AchievementManager had until now only supported
one caller registering a callback, and it didn't have any
synchronization. This isn't a problem for DolphinQt, but the PR to add
Android support for RetroAchievements exposes these problems. Let's
replace it with HookableEvent, which can handle all of this.

Remove window hints clearing the flag Qt::WindowContextHelpButtonHint,
which is already off by default in Qt 6.

In Qt 5 this flag was set by default for QDialogs, and on Windows put a
? button in the corner of the title bar allowing users to activate Qt's
QWhatsThis help system for a given widget. Since we don't set that text
the ? button was useless and so we hid it manually.

Some refactoring done to hardcore toggling so that it's more readily available for the toggle hardcore event.

Emergency PR to disable the leaderboards tab for launch if we are not satisfied with its testing yet.