Add R8 support

Add support for R8 to optimize apps and java libraries.

Test: m checkbuild
Change-Id: I2afd5d7a84912d3ab613c32c599bd1ebe60562e0

java/java_test.go

@@ -157,6 +157,9 @@ func testContext(config android.Config, bp string,
 
 		"build/soong/scripts/jar-wrapper.sh": nil,
 
+		"build/make/core/proguard.flags":             nil,
+		"build/make/core/proguard_basic_keeps.flags": nil,
+
 		"jdk8/jre/lib/jce.jar": nil,
 		"jdk8/jre/lib/rt.jar":  nil,
 	}