Do glic api gating in glic_api_host.ts

This migrates api gating code from c++ to ts.
Request types are annotated with a backgroundAllowed
property (defaults to false), which determines whether
the request should be allowed while glic is backgrounded.

If a request is not allowed:
* Requests incoming to the host are handled based on
  rules in BACKGROUND_RESPONSES, which should be nearly equivalent
  to the existing behavior today.
* Requests sent to the client must be sent with one of the
  following: sendWhenActive(), sendIfActiveOrDrop(),
  sendLatestWhenActive().

This ensures authors consider background behavior when
adding new messages, and automates the queuing logic.

Bug: b:434719445
Change-Id: I35f47cccf89c743854f893e96acc0b4a8ca7e435
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6854366
Commit-Queue: Dan Harrington <harringtond@chromium.org>
Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1505932}