### Godot version

4.2.dev 80de898d721f952dac0b102d48bb73d6b02ee1e8

### System information

OpenXR

### Issue description

The Godot 3 OpenXR plugin supported obtaining boundary/guardian information in order to obtain play space logic. While we do have a function in the `XRInterface` in Godot 4 that is supposed to retrieve this information (`get_play_area`) it is not implemented on the Godot 4 `OpenXRInterface`.

This logic needs to be ported.

### Steps to reproduce

Call `get_play_area`, be amazed by it not returning data :P

### Minimal reproduction project

Any XR project.
if (openxr_api) {
		XrEnvironmentBlendMode oxr_blend_mode;
		switch (mode) {
			case XR_ENV_BLEND_MODE_OPAQUE:
				oxr_blend_mode = XR_ENVIRONMENT_BLEND_MODE_OPAQUE;
				break;
			case XR_ENV_BLEND_MODE_ADDITIVE:
				oxr_blend_mode = XR_ENVIRONMENT_BLEND_MODE_ADDITIVE;
				break;
			case XR_ENV_BLEND_MODE_ALPHA_BLEND:
				oxr_blend_mode = XR_ENVIRONMENT_BLEND_MODE_ALPHA_BLEND;
				break;
			default:
				WARN_PRINT("Unknown blend mode requested: " + String::num_int64(int64_t(mode)));
				oxr_blend_mode = XR_ENVIRONMENT_BLEND_MODE_OPAQUE;
		}
		return openxr_api->set_environment_blend_mode(oxr_blend_mode);
	}
	return false;
}
void OpenXRInterface::on_state_ready() {
	emit_signal(SNAME("session_begun"));
}
void OpenXRInterface::on_state_visible() {
	emit_signal(SNAME("session_visible"));
}
void OpenXRInterface::on_state_focused() {