Utilize from-text stub module in build

Replace `android_stubs_current` with `android_from_text_stubs_current`,
a java_api_library module that creates from-text stubs. This feature is
hidden behind a flag `--build-from-text-stub`, which sets the env var
`ANDROID_PUBLIC_STUBS` as `android_from_text_stubs_current`.

Test: m --build-from-text-stub
Bug: 271154441
Change-Id: I06be32d9b7b9a54c0384010457406cabfff98c61
diff --git a/build/Android.mk b/build/Android.mk
index bdfc1d7..9c1d7b5 100644
--- a/build/Android.mk
+++ b/build/Android.mk
@@ -51,7 +51,7 @@
 # ===== SDK jar file of stubs =====
 # A.k.a the "current" version of the public SDK (android.jar inside the SDK package).
-full_target := $(call intermediates-dir-for,JAVA_LIBRARIES,android_stubs_current,,COMMON)/classes.jar
+full_target := $(call intermediates-dir-for,JAVA_LIBRARIES,$(ANDROID_PUBLIC_STUBS),,COMMON)/classes.jar
 full_src_target := $(call intermediates-dir-for,ETC,frameworks-base-api-current.srcjar)/frameworks-base-api-current.srcjar
 # android.jar is what we put in the SDK package.