Auto merge of #21799 - codehag:bug_1172897_rename_tab_actor, r=jdm

Bug 1172897 - Rename Tab Actor to BrowsingContextActor

As part of [Bug 1172987](https://bugzilla.mozilla.org/show_bug.cgi?id=1172897) we renamed TabActor, as the actor does not represent tabs (as in a browser tab), it instead represents a browsing context as defined by the the [HTML standard](https://html.spec.whatwg.org/multipage/browsers.html#windows). In a later PR I will mirror the structure we have on devtools to have a targets folder, which contains all target types. At the moment it looks like servo only represents workers and browsing contexts.

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- [ ] `./mach build -d` does not report any errors
Unfortunately, I am unable to build due to #21792 -- I will try to find a linux machine to build on
- [x] `./mach test-tidy` does not report any errors
- [x] These changes fix Bugzilla [Bug 1172987](https://bugzilla.mozilla.org/show_bug.cgi?id=1172897).

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- [x] These changes do not require tests because this is a renaming and shouldn't impact tests as far as I can tell

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