Support direct preview buffer sizing and YUV capture format in host fixtures

tools/chatgui-android/video-tests/src/main/kotlin/android/graphics/ImageFormat.kt

@@ -0,0 +1,3 @@
+package android.graphics
+
+object ImageFormat { const val YUV_420_888 = 35 }

tools/chatgui-android/video-tests/src/main/kotlin/android/graphics/SurfaceTexture.kt

@@ -7,6 +7,7 @@ class SurfaceTexture(val id: Int) {
     var releaseCalls = 0
         private set
     var failures = emptySet<String>()
+    fun setDefaultBufferSize(width: Int, height: Int) { check("buffer" !in failures && width > 0 && height > 0) }
     fun release() {
         releaseCalls++; check("release" !in failures) { "texture release failed" }
         released = true; check("release after" !in failures) { "texture release failed after effect" }