Currently AFAICT we don't have a way to get the MCP server socket after
it started. So this change introduces a new `protocol-server` subcommand
that allows us to query the location of a running server:
```
(lldb) protocol-server start MCP listen://localhost:0
MCP server started with connection listeners: connection://[::1]:36051, connection://[127.0.0.1]:36051
(lldb) protocol-server get MCP
MCP server connection listeners: connection://[::1]:36051, connection://[127.0.0.1]:36051
(lldb) protocol-server stop MCP
(lldb) protocol-server get MCP
error: MCP server is not running
```
It looks like #146603 broke the
[lldb-remote-linux-win](https://lab.llvm.org/buildbot/#/builders/197)
build bot because `MCPUnixSocketCommandTestCase` is trying to start a
protocol-server via unix domain sockets on windows.
This change makes it so the test is skipped if it is remote.
When starting an MCP protocol server that uses unix sockets as the
transport, a local `'[0.0.0.0]:0'` file is used instead of the supplied
socket path, e.g:
```
(lldb) protocol-server start MCP accept:///tmp/some/path.sock
MCP server started with connection listeners: unix-connect://[0.0.0.0]:0
(lldb) shell ls '[*'
[0.0.0.0]:0
```
This change makes it so that the URI path is used if the socket protocol
is `ProtocolUnixDomain`:
```
(lldb) protocol-server start MCP accept:///tmp/some/path.sock
MCP server started with connection listeners: unix-connect:///tmp/some/path.sock
```
