Add `frame_ancestor_relation` to `net::IsolationInfo`

This change adds a new field to `net::IsolationInfo` called
`frame_ancestor_relation`, which is primarily calculated in
`RenderFrameHostImpl::ComputeIsolationInfoInternal`, similar to
`net::SiteForCookies`. This tracks the relationship between a
a request and all of its frame's ancestors which will allow us to
add a new `Sec-Fetch-Frame-Ancestors` header in a follow-up CL:
http://crrev.com/c/6523763

This patch was originally drafted by sledoux@chromium.org
(@sjledoux on GitHub): http://crrev.com/c/6199199

Bug: 398224102
Change-Id: I5d3ab9cfbfba1f68ebae8ee2959a55bbe6b10394
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6499507
Reviewed-by: Giovanni Ortuno Urquidi <ortuno@chromium.org>
Reviewed-by: Chris Fredrickson <cfredric@chromium.org>
Reviewed-by: mmenke <mmenke@chromium.org>
Commit-Queue: Joshua Thomas <masnoble@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1466645}