Split BlurFilter into interface + implementation

With the first implementation being KawaseBlurFilter, which was
previously in BlurFilter.cpp.

Bug: 185365391
Test: atest BlurTests
Change-Id: I265ec54a1a2e047b22d191c37bcb788f92ad0672
diff --git a/libs/renderengine/skia/SkiaGLRenderEngine.cpp b/libs/renderengine/skia/SkiaGLRenderEngine.cpp
index d5ec774..e6fb94d 100644
--- a/libs/renderengine/skia/SkiaGLRenderEngine.cpp
+++ b/libs/renderengine/skia/SkiaGLRenderEngine.cpp
@@ -53,6 +53,7 @@
 #include "SkBlendMode.h"
 #include "SkImageInfo.h"
 #include "filters/BlurFilter.h"
+#include "filters/KawaseBlurFilter.h"
 #include "filters/LinearEffect.h"
 #include "log/log_main.h"
 #include "skia/debug/SkiaCapture.h"
@@ -328,7 +329,7 @@
 
     if (args.supportsBackgroundBlur) {
         ALOGD("Background Blurs Enabled");
-        mBlurFilter = new BlurFilter();
+        mBlurFilter = new KawaseBlurFilter();
     }
     mCapture = std::make_unique<SkiaCapture>();
 }