ButtonManager is very different from how a normal input backend works,
and is making it hard for us to improve controller support on Android.
The following commits will add a new input backend in its place.

Obsoletes these functions in favor of the standard member functions
added in C++20.

This is the first step of getting rid of the controller indirection
on Android. (Needing a way for touch controls to provide input
to the emulator core is the reason why the controller indirection
exists to begin with as far as I understand it.)

SPDX standardizes how source code conveys its copyright and licensing
information. See https://spdx.github.io/spdx-spec/1-rationale/ . SPDX
tags are adopted in many large projects, including things like the Linux
kernel.

fix some related grammar errors
only the ButtonManager required code changes

Fix -Winconsistent-missing-override warnings on Android

Currently, the touch controller overlay uses a square gate for
sticks. This commit changes that so that it instead uses the
stick gate configured in the INI, which ensures that the values
sent to the core are appropriately scaled regardless of what
is configured in the INI and makes the overlay look nicer
if the INI is set to a stick gate that matches the graphics.

Device id is "" on ChromeOS when using gamepad