Fetching artifacts from the build server doesn't go well with large
numbers of files in nested directories.
Produce an additional rustdoc.zip artifact to make this easier.
This change also prevents ${DIST} from receiving the unpacked rustdoc
site. This can be changed if b/188822051 is fixed.
Bug: 162741284
Test: m rustdoc; check resulting zip contents manually
Change-Id: I80b6a8fa6e274d2d8c3419d8734251afd4d7dba7
Adds `m rustdoc` which generates documentation for all Rust libraries
to $OUT_DIR/soong/rustdoc.
Follow up work:
* Generate an index page that lists all modules.
* Preserve the artifacts so we can have an always-up-to-date go link.
Test: m rustdoc
Bug: None
Change-Id: Id2d6b9cbab5b02e36b575567563d7cc7606b9401
