Adds a workaround to fix version inconsistency

frameworks/base still has the tree on R while the build system considers
current development to be S which causes issues when Robolectric goes
looking for an R jar but instead finds an S jar.  Therefore, for the
moment, we are hardcoding this to be tagged as R. In the future,
hopefully these two sources of truth can be aligned better.

Bug: b/157635117
Test: N/A or manual
Change-Id: I7495735b1c6c4369408bdf8805f59fad6aac5128