* This adjusts the `Request`/`Response` types to have an `id` that is
either a string or a number.
* Merges 'Error' into 'Response' to have a single response type that
represents both errors and results.
* Adjusts the `Error.data` field to by any JSON value.
* Adds `operator==` support to the base protocol types and simplifies
the tests.
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.
