Add build rule to merge annotation zips

This target produces nearly identical contents to the build target
framework-doc-stubs (the only diffs are in whitespace). Using this
module in the SDK zip will allow changing the inputs of
framework-doc-stubs to java sources that don't have all the annotations
(the jar stubs).

Bug: 187397779
Test: m sdk-annotations.zip and diff with framework-doc-stubs zip
Change-Id: Id163473c455f25c5f31c965d907c0c3b0e7755fc