Expose MCP provenance to tool lifecycle extensions (#40976)

## What changed

- Add optional `McpToolContext` metadata to `ToolStartInput`, exposing the
  model-visible MCP tool details and its source classification without exposing
  the executable client.
- Classify MCP calls as connectors, configured servers, plugin servers,
  executor-selected plugins, or other registrations based on the prepared call.
- Prepare each MCP call before notifying tool lifecycle contributors and reuse
  that same call for execution so the callback describes the call that runs.

## Testing

- Cover host-owned connector calls and extension-owned Apps server calls,
  including their distinct provenance and executed tool names.

GitOrigin-RevId: efd23f511b1045ffdd96349d621ad62365569b2b