[3.2] Support SDL2 half axes and inverted axes mappings.

[madmiraal]

This is a partial backport of #38151. It includes the parsing and implementation of SDL game controller half axis and inverted axis entries. However, to make this a non-breaking change the following have not been implemented:

• The triggers remain as buttons and not axes. Therefore any axes that map to the triggers will be treated as buttons and not axes.
• The Input Mappings have not been fixed, because there remains no way within Godot to differentiate between buttons and axes.

Note: I don't have a game controller to test it with; so it will need to be tested by those that do. To parse the previously excluded entries, requires deleting main/default_controller_mappings.gen.cpp so it can be recreated.

Below is an updated 3.2 version of @akien-mga's joypad test project, which includes includes highlighting the axes (except the triggers) activated on the joypad:
Joypads.zip

[madmiraal]

Rebased following 7bf9787.

[akien-mga]

Tested locally with my generic PS3 controller, the https://github.com/godotengine/godot-demo-projects/tree/master/misc/joypads demo works well without regression.

Let's merge, and I'll ask for wide testing of controllers when I publish 3.2.3 beta 1 in coming days.

[akien-mga]

Thanks!