This PR moves the MCP protocol code into its own library
(`lldbProtocolMCP`) so the code can be shared between the
`ProtocolServerMCP` plugin in LLDB as well as `lldb-mcp`. The goal is to
do the same thing for DAP (which, for now, would be used exclusively
from `lldb-dap`).
To make it clear that it's neither part of the `lldb` nor the
`lldb_private` namespace, I created a new `lldb_protocol` namespace.
Depending on how much code would be reused by lldb-dap, we may move more
code into the protocol library.
ed294c28ac