TAS Input: Enable emulator hotkeys and controller input when TAS Input window has focus

CMake: Put all unit tests in one binary

We currently have 32 different binaries containing unit tests. At least
when I build for Android, each one takes up over 200 MiB, and linking
them all increases my incremental build times by over a minute. I'd
like to change this for the sake of my productivity and disk space.

For reference, MSBuild is already putting all tests in a single binary.

Enable emulator hotkeys and controller input (when that option is
enabled) when a TAS Input window has focus, as if it was the render
window instead.  This allows TASers to use frame advance and the like
without having to switch the focused window or disabling Hotkeys Require
Window Focus which also picks up keypresses while other apps are active.

Cursor updates are disabled when the TAS Input window has focus, as
otherwise the Wii IR widget (and anything else controlled by the mouse)
becomes unusable. The cursor continues to work normally when the render
window has focus.

Eliminate SettingsHandler's `SetBytes` and `Reset` methods

Also make the `Decrypt` method private.

As far as I can tell, the only motivation for exposing the `SetBytes`
and `Reset` methods is to allow `CBoot::SetupWiiMemory` to use the same
`SettingsHandler` instance to read settings data and then write it back.
It seems cleaner to just use two separate instances, and require a given
`SettingsHandler` instance to be used for either writing data to a
buffer or reading data from a buffer, but not both.

A natural next step is to split the `SettingsHandler` class into two
classes, one for writing data and one for reading data. I've deferred
that change for a future PR.