[Captured Sites] Refactor control script to allow broader usage.

In order to integrate with bisect scripts, change captured sites commands to a library or different command types that can allow a
caller to use in additional ways.

Also add some test verification to script correctness.

The diff is very unclean but this is intended to not have any
functionality change yet (other than the tests).

Bug: 348671533
Change-Id: I0b3be7118c08ac537a832beee50dcdbe12517b3f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5703796
Reviewed-by: Sven Zheng <svenzheng@chromium.org>
Commit-Queue: Ian Struiksma <ianstruiksma@google.com>
Cr-Commit-Position: refs/heads/main@{#1327031}