Deeper sanity checking of emitted types.

When emitting a method or field, verify that we're able to reference
all mentioned types.  This ensures that we don't accidentally
reference undefined classes/interfaces.

Test: manual inspection of API files
Bug: 69791141
Change-Id: I84e0c87fe83daa118661f61dbdf17b58ea5282d4
Merged-In: I84e0c87fe83daa118661f61dbdf17b58ea5282d4