Add R8 support to Soong.

Move R8_COMPAT_PROGUARD definition to Soong.
Copy the proguard_dictionary file so that the find
command that builds proguard_dict.zip can find it.

Test: m checkbuild
Change-Id: I28b2fce26ccb6225be0bd71802a43fe63df85daa
diff --git a/core/clear_vars.mk b/core/clear_vars.mk
index e9c07df..b4a03ea 100644
--- a/core/clear_vars.mk
+++ b/core/clear_vars.mk
@@ -232,6 +232,7 @@
 LOCAL_SOONG_DEX_JAR :=
 LOCAL_SOONG_HEADER_JAR :=
 LOCAL_SOONG_JACOCO_REPORT_CLASSES_JAR :=
+LOCAL_SOONG_PROGUARD_DICT :=
 LOCAL_SOONG_RESOURCE_EXPORT_PACKAGE :=
 LOCAL_SOONG_RRO_DIRS :=
 # '',true