Add a Steam Frame build type with the Khronos OpenXR loader

The Frame runs Android apps in a container (Lepton) that has no OpenXR
loader broker, so the APK needs its own loader. This adds a "frame" build
type: ./gradlew assembleFrame.

It's release plus:
- applicationId .frame, minSdk 30 (the container is Android 11)
- a manifest overlay that drops the headtracking requirement and the
  Quest/Pico metadata, since the install fails with it
- the Khronos loader 1.1.63, fetched from Maven Central at build time,
  checked against a SHA-256 and unpacked into build/ (not committed)
- L1VR_STEAM_FRAME for the native code, BuildConfig.STEAM_FRAME for Java

Quest builds don't see any of this. I also added the gradle wrapper script
to Projects/Android, since the wrapper jar and properties were already
there, and -Wall for the VR sources.

Haven't run it on the headset yet.

java/com/drbeef/lambda1vr/GLES3JNIActivity.java

@@ -49,13 +49,26 @@ import static android.system.Os.setenv;
 			manufacturer = "meta";
 		}
 
-		try
+		if (BuildConfig.STEAM_FRAME)
 		{
-			//Load manufacturer specific loader
-			System.loadLibrary("openxr_loader_" + manufacturer);
-			setenv("OPENXR_HMD", manufacturer, true);
-		} catch (Exception e)
-		{}
+			//The Frame has no loader broker, so the Khronos loader is in the APK
+			System.loadLibrary("openxr_loader");
+			try
+			{
+				setenv("OPENXR_HMD", "steamframe", true);
+			} catch (Exception e)
+			{}
+		}
+		else
+		{
+			try
+			{
+				//Load manufacturer specific loader
+				System.loadLibrary("openxr_loader_" + manufacturer);
+				setenv("OPENXR_HMD", manufacturer, true);
+			} catch (Exception e)
+			{}
+		}
 
 		System.loadLibrary( "xash" );
 	}