COOP: restrict-properties 3/*: CoopRelatedGroup

This is the core patch of the COOP: restrict-properties
implementation. It introduces an important abstraction, the
CoopRelatedGroup. It represents a grouping of BrowsingContext groups
(BrowsingInstance) that are capable of a limited set of asynchronous
interactions, namely postMessage and closed.

It is built as closely as possible to how BrowsingInstance is built
on SiteInstance:
- It is fully private, and interacted with through SiteInstance and
  BrowsingInstance. SiteInstance exposes a single new method,
  GetCoopRelatedSiteInstance(), that works similarly to the
  GetRelatedSiteInstance() method, but at the CoopRelatedGroup level.
- It is collectively owned by the BrowsingInstances that are part of
  it. A register/unregister mechanism is used to know about the
  BrowsingInstances that are still part of the group.
- It might reuse an existing BrowsingInstance when necessary, similar
  to how SiteInstance's are reused within a BrowsingInstance.

To support BrowsingInstance reuse, some information needs to be
available to the CoopRelatedGroup when doing the selection. In
particular it needs to know whether the BrowsingInstance
hosts COOP: restrict-properties pages, and from which origin. We
record that information from the NavigationRequest into UrlInfo.

The SiteInstance picking algorithm is updated to output a SiteInstance
created via GetCoopRelatedSiteInstance() when a
BrowsingContextGroupSwap::kCoopRelatedSwap is requested.

Added browser tests and unit tests cover the newly introduced code.

Bug: 1221127, 1385827
Change-Id: Ief8436b5d532b6aadc5d9a29d94346e3fae2641c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3948564
Commit-Queue: Arthur Hemery <ahemery@chromium.org>
Reviewed-by: Charlie Reis <creis@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1112861}