It's not necessary on posix platforms as of #126935 and it's ignored on
windows as of #138896. For both platforms, we have a better way of
inheriting FDs/HANDLEs.

This PR adds an MCP (Model Context Protocol ) server to LLDB. For
motivation and background, please refer to the corresponding RFC:
https://discourse.llvm.org/t/rfc-adding-mcp-support-to-lldb/86798

I implemented this as a new kind of plugin. The idea is that we could
support multiple protocol servers (e.g. if we want to support DAP from
within LLDB). This also introduces a corresponding top-level command
(`protocol-server`) with two subcommands to `start` and `stop` the
server.

```
(lldb) protocol-server start MCP tcp://localhost:1234
MCP server started with connection listeners: connection://[::1]:1234, connection://[127.0.0.1]:1234
```

The MCP sever supports one tool (`lldb_command`) which executes a
command, but can easily be extended with more commands.

Replace (questionable) header globs with an explicit argument supported
by llvm_add_library.

If we're not touching them, we don't need to do anything special to pass
them along -- with one important caveat: due to how cmake arguments
work, the implicitly passed arguments need to be specified before
arguments that we handle.

This isn't particularly nice, but the alternative is enumerating all
arguments that can be used by llvm_add_library and the macros it calls
(it also relies on implicit passing of some arguments to
llvm_process_sources).

This fixes a data race between the main thread and the default event
handler thread. The statusline format option value was protected by a
mutex, but it was returned as a pointer, allowing one thread to access
it while another was modifying it.

Avoid the data race by returning format values by value instead of by
pointer.

A few files of lldb dir & few other files had duplicate headers
included. This patch removes those redundancies.

---------

Co-authored-by: Akash Agrawal <akashag@qti.qualcomm.com>

Use the current frame's language to lookup commands provided by language plugins.

This means commands like `language {objc,cplusplus} <command>` can be used directly, without using the `language <lang>` prefix.

For example, when stopped on a C++ frame, `demangle _Z1fv` will run `language cplusplus demangle _Z1fv`.

rdar://149882520

Fix typo in interpreter property description.

Fixes #140708

std::string::find accepts anything that can be converted to
std::string_view starting in C++17.  Since StringRef can be converted
to std::string_view, we do not need to create a temporary instance of
std::string here.