### Godot version

4.1

### System information

Windows 10 - Godot 4.1.1 - Compatibility

### Issue description

When trying to use the Varjo XR3 headset (in OpenXR mode) with Godot 4 (with OpenXR and passthrough activated), the passthrough does not work, i.e. the scene is rendered on a black background instead of the camera stream.

It seems to me that are two problems in the openxr module, more precisely in the openx_api.cpp file (fixing them solves  the issue) : 

1. The XR_COMPOSITION_LAYER_BLEND_TEXTURE_SOURCE_ALPHA_BIT  is only set when the number of layers is > 1, which is fine for the Meta Quest headset but does not work for the Varjo since it only requires one layer. 
2. The environment blend mode XR_ENVIRONMENT_BLEND_MODE_ALPHA_BLEND  is only really set when the XRFbPassthrough extension is present, which is not the case with the Varjo runtime. 

I am not sure how to fix this without causing issues for other headsets.

1. Would it be an issue to always activate the XR_COMPOSITION_LAYER_BLEND_TEXTURE_SOURCE_ALPHA_BIT ? 
2. Could blend modes be activated even if they are not supported by an extension ? 





### Steps to reproduce

- Create a Godot 4 project with OpenXR activated in Compatibility mode
- Add the code to activate OpenXr and to enable passthrough : https://docs.godotengine.org/en/stable/tutorials/xr/openxr_passthrough.html#passthrough-extension
- Start the Varjo Base software and activate OpenXR
- Run the Godot project

### Minimal reproduction project

N/A
}
		if (!text_driver_options.is_empty() && text_driver_options.find(",") == -1) {
			/
			text_driver_options += ",";
		}
		text_driver_options += driver_name;
	}
	ProjectSettings::get_singleton()->set_custom_property_info(PropertyInfo(Variant::STRING, "internationalization/rendering/text_driver", PROPERTY_HINT_ENUM, text_driver_options));
	/
	if (text_driver.is_empty()) {
		text_driver = GLOBAL_GET("internationalization/rendering/text_driver");
	}
	if (!text_driver.is_empty()) {
		/
		for (int i = 0; i < TextServerManager::get_singleton()->get_interface_count(); i++) {
			if (TextServerManager::get_singleton()->get_interface(i)->get_name() == text_driver) {
				text_driver_idx = i;
				break;
			}
		}
	}
	if (text_driver_idx < 0) {
		/
		int max_features = 0;
		for (int i = 0; i < TextServerManager::get_singleton()->get_interface_count(); i++) {
			uint32_t features = TextServerManager::get_singleton()->get_interface(i)->get_features();
			int feature_number = 0;
			while (features) {
				feature_number += features & 1;
				features >>= 1;