Adds new utilities that make it easier to write test cases for lldb acting as a client over a gdb-remote connection.
- A GDBRemoteTestBase class that starts a mock GDB server and provides an easy way to check client packets
- A MockGDBServer that, via MockGDBServerResponder, can be made to issue server responses that test client behavior.
- Utility functions for handling common data encoding/decoding
- Utility functions for creating dummy targets from YAML files
Split from the review at https://reviews.llvm.org/D42145, which was a new feature that necessitated the new testing capabilities.