When reducing the number of Connecter Controllers, keep the one clicked if it was not the last one of the list

[REUSE] is a specification that aims at making file copyright
information consistent, so that it can be both human and machine
readable. It basically requires that all files have a header containing
copyright and licensing information. When this isn't possible, like
when dealing with binary assets, generated files or embedded third-party
dependencies, it is permitted to insert copyright information in the
`.reuse/dep5` file.

Oh, and it also requires that all the licenses used in the project are
present in the `LICENSES` folder, that's why the diff is so huge.
This can be done automatically with `reuse download --all`.

The `reuse` tool also contains a handy subcommand that analyzes the
project and tells whether or not the project is (still) compliant,
`reuse lint`.

Following REUSE has a few advantages over the current approach:

- Copyright information is easy to access for users / downstream
- Files like `dist/license.md` do not need to exist anymore, as
  `.reuse/dep5` is used instead
- `reuse lint` makes it easy to ensure that copyright information of
  files like binary assets / images is always accurate and up to date

To add copyright information of files that didn't have it I looked up
who committed what and when, for each file. As yuzu contributors do not
have to sign a CLA or similar I couldn't assume that copyright ownership
was of the "yuzu Emulator Project", so I used the name and/or email of
the commit author instead.

[REUSE]: https://reuse.software

Follow-up to 01cf05bc

Co-authored-by: Its-Rei <kupfel@gmail.com>

Abstracts most of the input mechanisms under an InputSubsystem class
that is managed by the frontends, eliminating any static constructors
and destructors. This gets rid of global accessor functions and also
allows the frontends to have a more fine-grained control over the
lifecycle of the input subsystem.

This also makes it explicit which interfaces rely on the input subsystem
instead of making it opaque in the interface functions. All that remains
to migrate over is the factories, which can be done in a separate
change.

Co-authored-by: James Rowe <jroweboy@gmail.com>
Co-authored-by: Its-Rei <kupfel@gmail.com>

To prepare for translation support, this makes all of the widgets
cognizant of the language change event that occurs whenever
installTranslator() is called and automatically retranslates their text
where necessary.

This is important as calling the backing UI's retranslateUi() is often
not enough, particularly in cases where we add our own strings that
aren't controlled by it. In that case we need to manually refresh the
strings ourselves.

The previous code could potentially be a compilation issue waiting to
occur, given we forward declare the type for a std::unique_ptr. If the
complete definition of the forward declared type isn't visible in a
translation unit that the class is used in, then it would fail to
compile.

Defaulting the destructor in a cpp file ensures the std::unique_ptr's
destructor is only invoked where its complete type is known.

This doesn't depend on any part of the private interface, so it can be
made a non-member internal function.

This moves the actual button configuration to a separate dialog and only has the enabled and type controls in the tab.

* get rid of boost::optional

* Remove optional references

* Use std::reference_wrapper for optional references

* Fix clang format

* Fix clang format part 2

* Adressed feedback

* Fix clang format and MacOS build

* Added a context menu on the buttons including Clear & Restore Default

* Allow clearing (unsetting) inputs. Added a Clear All button

* Allow restoring a single input to default (instead of all)

* Removed use of raw QTimer* pointer.
* Update to use type-safe QObject::connect.
* getKeyName can be a static local function.
* Prefer to use function arguments instead of member variables.
* Store Qt::Key instead of converting string back into keycode.

This makes clang-format useful on those.

Also add a bunch of forgotten transitive includes, which otherwise
prevented compilation.