Make string matching the last resort way to look up types

That is, Find(const AidlType&) will call FindByName(const std::string&)
rather than the other way around.  Later we'll use annotations in the
AidlType to pick one of several different type name strings.

Bug: 26729450
Test: unittests continue to pass

Change-Id: I10fcb88eabda30b88d5457ecfc8931755a0aa872
7 files changed