[lldb-mcp] Adding a tool to list debuggers again. (#158340)

This brings back the tool for listing debuggers.

This is helpful when an LLM doesn't support resources, like gemini-cli.

I also fixed an issue with `ServerInfoHandle` not always cleaning up the
`~/lldb/lldb-mcp-<pid>.json` file correctly.

GitOrigin-RevId: ec8819f1858a67cff20ca47e0cbfa11e292c989f
5 files changed