Android: Add helper class for generating OpenGL shaders

This CL adds a helper class GlShaderBuilder to build an instances of
RendererCommon.GlDrawer that can accept multiple input sources
(OES, RGB, or YUV) using a generic fragment shader as input.

Bug: webrtc:9355
Change-Id: I14a0a280d2b6f838984f7b60897cc0c58e2a948a
Reviewed-on: https://webrtc-review.googlesource.com/80940
Commit-Queue: Magnus Jedvert <magjed@webrtc.org>
Reviewed-by: Sami Kalliomäki <sakal@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#23622}

sdk/android/api/org/webrtc/RendererCommon.java

@@ -31,7 +31,12 @@ public class RendererCommon {
     public void onFrameResolutionChanged(int videoWidth, int videoHeight, int rotation);
   }
 
-  /** Interface for rendering frames on an EGLSurface. */
+  /**
+   * Interface for rendering frames on an EGLSurface with specified viewport location. Rotation,
+   * mirror, and cropping is specified using a 4x4 texture coordinate transform matrix. The frame
+   * input can either be an OES texture, RGB texture, or YUV textures in I420 format. The function
+   * release() must be called manually to free the resources held by this object.
+   */
   public static interface GlDrawer {
     /**
      * Functions for drawing frames with different sources. The rendering surface target is