Unzip offline-sdk-docs for m offline-sdk-docs or m docs

offline-sdk-docs is the most useful target for local developers
verifying documentation changes.  Unzip offline-sdk-docs.zip
into out/target/common/docs/offline-sdk/ whenever the offline-sdk-docs
or docs targets are built.

Fixes: 124115897
Test: m offline-sdk-docs
Change-Id: I92ce65742e7475cc64a688f2b1893c96ecfd2a52

Android.mk

@@ -72,6 +72,9 @@ $(OUT_DOCS)/offline-sdk-timestamp: $(OUT_DOCS)/offline-sdk-docs-docs.zip
 	$(hide) mkdir -p $(OUT_DOCS)/offline-sdk
 	( unzip -qo $< -d $(OUT_DOCS)/offline-sdk && touch -f $@ ) || exit 1
 
+.PHONY: docs offline-sdk-docs
+docs offline-sdk-docs: $(OUT_DOCS)/offline-sdk-timestamp
+
 # Run this for checkbuild
 checkbuild: doc-comment-check-docs
 # Check comment when you are updating the API