Make the FindTypes(std::vector<CompilerContext>, ...) API testable in lldb-test

This adds a -compiler-context=<...> option to lldb-test that trakes a
comma-separated string that is a list of kind/name pairs and
translates it into a std::vector<CompilerContext>, a CompilerContext
being a pair of context-kind and name.

Differential Revision: https://reviews.llvm.org/D66453

<rdar://problem/54471165>

llvm-svn: 369407