[lldb/Reproducers] Support reproducers for PlatformRemoteGDBServer

Add reproducer support to PlatformRemoteGDBServer. The logic is
essentially the same as for ProcessGDBRemote. During capture we record
the GDB packets and during replay we connect to a replay server.

This fixes TestPlatformClient.py when run form a reproducer.

Differential Revision: https://reviews.llvm.org/D80224