Add LOCAL_AAPT2_ONLY

This allows modules to specify that they may only be used from modules
using aapt2. Using aapt2 removes absolute path references to modules, so
this can be useful if a module is preparing to move its sources, or
replace itself with a prebuilt aar.

Test: m
Test: Label frameworks/support/design; m
Test: Label frameworks/support/v4; m
Test: build/soong/build_test.bash
Change-Id: Icfb3d4b19a6a0e3a3bb00091d2a97a4d88c0c761
diff --git a/core/package_internal.mk b/core/package_internal.mk
index 9bf173f..9f99c7a 100644
--- a/core/package_internal.mk
+++ b/core/package_internal.mk
@@ -146,6 +146,10 @@
 need_compile_asset := true
 endif
 
+ifdef LOCAL_AAPT2_ONLY
+LOCAL_USE_AAPT2 := true
+endif
+
 my_res_package :=
 ifdef LOCAL_USE_AAPT2
 # In aapt2 the last takes precedence.