API txt files are dist artifacts

API txt files from a java_sdk_library are automatically registered as
dist artifacts for sdk and win_sdk targets.

They are installed under $(DIST_DIR)/apistubs/<apiscope>/api/<name>.txt
where <apiscope> can be public, system and test.

Bug: 77577799
Test: m -j
Change-Id: I38cd8ee000445ce843ac01ead38001e509228738