Add documentation for JavaClassWrapper and AndroidRuntime plugin

[m4gr3d]

As the title mentions, this adds documentation for the JavaClassWrapper singleton and the AndroidRuntime plugin.
These capabilities were introduced in Godot 4.4, so the PR will need to be pick against the 4.4 documentation as well.

[dsnopek]

Looks good to me!

[Alex2782]

The examples worked.

On my Samsung Tab, I had reduced the system vibration level, and after increasing it, the example worked as well.

[mhilbrunner]

Maybe this list should be just part of the previous paragraph, to keep it shorter? "..diverse functionality, like push notifications, analytics, authentication, ads etc."? Or similar. Don't care strongly about this however.

[syntaxerror247]

Let's also add a line about inner classes with an example.
You can use this example:

var version = JavaClassWrapper.wrap("android.os.Build$VERSION")
var sdk_int = version.SDK_INT
If sdk_int == 30:
    # Do something specific on android 11 devices.
else:
    # All other devices