[lldb] Expose debuggers and target as resources through MCP (#148075)

Expose debuggers and target as resources through MCP. This has two
advantages:

1. Enables returning data in a structured way. Although tools can return
structured data with the latest revision of the protocol, we might not
be able to update before the majority of clients has adopted it.
2. Enables the user to specify a resource themselves, rather than
letting the model guess which debugger instance it should use.

This PR exposes a resource for debuggers and targets.

The following URI returns information about a given debugger instance:

```
lldb://debugger/<debugger id>
```

For example:

```
{
  uri: "lldb://debugger/0"
  mimeType: "application/json"
  text: "{"debugger_id":0,"num_targets":2}"
}
```

The following URI returns information about a given target:

```
lldb://debugger/<debugger id>/target/<target id>
```

For example:

```
{
  uri: "lldb://debugger/0/target/0"
  mimeType: "application/json"
  text: "{"arch":"arm64-apple-macosx26.0.0","debugger_id":0,"path":"/Users/jonas/llvm/build-ra/bin/count","target_id":0}"
}
```