[3.x] Simplify InputDefault::joy_axis code by using float instead of struct JoyAxis

[madmiraal]

Backport of #56238.

Although the 3.x branch does not have issue #44178, the fix contains significant code simplification and the removal of the misleading struct JoyAxis, which I think would be advantageous for 3.x too.

[akien-mga]

Worth noting that the code is different in the master branch (and thus not changed in #56238), I'm not sure if it means that either the 3.x or master version might be missing a follow-up fix? @dsnopek @Faless

In master it's:

                int *axes = godot_webxr_get_controller_axes(p_controller_id);
                if (axes) {
                        // TODO again just a temporary fix, split these between proper float and vector2 inputs
                        for (int i = 0; i < axes[0]; i++) {
                                char name[1024];
                                sprintf(name, "axis_%i", i);

                                float value = *((float *)axes + (i + 1));
                                ;
                                tracker->set_input(name, value);
                        }
                        free(axes);
                }

[akien-mga]

Thanks!