Make ToolRequest the API for ActorKeyedService

This converts the PerformActions API to take a vector of ToolRequest
objects which now serve as the API for tool calling in the
ActorKeyedService.

This CL moves the extension API to the new path as an example. A
future CL will move Glic and tests over as well.

Bug: 411462297
Change-Id: I620519f3ef066e36d5200b30156a344cc7ed41f1
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6715557
Reviewed-by: Kevin Graney <kmg@google.com>
Reviewed-by: Erik Chen <erikchen@chromium.org>
Commit-Queue: David Bokan <bokan@chromium.org>
Reviewed-by: Tom Sepez <tsepez@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1485161}