### 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 = openxr_api->get_environment_blend_mode();
		switch (oxr_blend_mode) {
			case XR_ENVIRONMENT_BLEND_MODE_OPAQUE: {
				return XR_ENV_BLEND_MODE_OPAQUE;
			} break;
			case XR_ENVIRONMENT_BLEND_MODE_ADDITIVE: {
				return XR_ENV_BLEND_MODE_ADDITIVE;
			} break;
			case XR_ENVIRONMENT_BLEND_MODE_ALPHA_BLEND: {
				return XR_ENV_BLEND_MODE_ALPHA_BLEND;
			} break;
			default:
				break;
		}
	}
	return XR_ENV_BLEND_MODE_OPAQUE;
}
bool OpenXRInterface::set_environment_blend_mode(XRInterface::EnvironmentBlendMode mode) {