add RuntimeXfermode API to the graphics platform

Flag: com.android.graphics.hwui.flags.runtime_color_filters_blenders

Test: atest CtsUiRenderingTestCases:RuntimeXfermodeTests
Bug: b/358126864

Change-Id: Idd15f937707feec51387b513b75cfadfaf0336a3
diff --git a/libs/hwui/Android.bp b/libs/hwui/Android.bp
index fcb7efc..e2db2c9 100644
--- a/libs/hwui/Android.bp
+++ b/libs/hwui/Android.bp
@@ -355,6 +355,7 @@
         "jni/AnimatedImageDrawable.cpp",
         "jni/Bitmap.cpp",
         "jni/BitmapRegionDecoder.cpp",
+        "jni/RuntimeXfermode.cpp",
         "jni/BufferUtils.cpp",
         "jni/HardwareBufferHelpers.cpp",
         "jni/BitmapFactory.cpp",