Add a verification step for typemap config

If there is a typo in the typemap config, this will raise a warning
telling the developer that a typemap has not been referenced.

Most of the change is mechanical (i.e.: removing dead typemaps that have
no effect).

This change will force typemaps to be declared in the mojom rule that
contains the mojom module where the type is declared, which is probably
better because having another target declare the typemaps can lead to
some very... interesting.. side effects. One of these side effects is
that the type of the generated code will look different, depending on
your deps.

Bug: 428039213
Change-Id: I75b40055cf9cc045b5e7890365550d846fb71145
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6692233
Owners-Override: Daniel Cheng <dcheng@chromium.org>
Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Commit-Queue: Fred Shih <ffred@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1484659}