ReshapeForShadowedProp should use the same mechanism to invalidate the shape teleporting optimization as ReshapeForProtoMutation. This is simpler, cleaner, and avoids dictionary mode conversions.

The dictionary conversion here was always a bit of a hack, one of the ReShape goals is to get rid of these dictionary conversions that don't have anything to do with property mutation.

This reverts the change in bug 1507433. Now that shape always implies prototype,
we don't need to check the objects between receiver and holder have the uncacheable-proto
flag. This simplifies the next parts.

The flag is now only used for the shape teleporting optimization so be more explicit
about this. The next patch will use this flag also for the shadowed-property case.

Depends on D118359

The flag is now used to guard against both cases teleporting has to watch out
for: proto changes and shadowed properties.

This lets us get rid of dictionary conversions and reshaping for ReshapeForShadowedProp.

Depends on D118360

Backed out 4 changesets (bug 1717438) for causing bc failures in browser_ext_browserAction_context.js.
https://hg.mozilla.org/integration/autoland/rev/6778252284f52fe00621915df01e65d8b2047088

Push with failures:
https://treeherder.mozilla.org/jobs?repo=autoland&revision=13111b300e29be7ef23aba990a330a1068dc1cf9&selectedTaskRun=OLZZp6cBQN6XUEEeQJzQEQ.0

Failure log:
https://treeherder.mozilla.org/logviewer?job_id=345290748&repo=autoland&lineNumber=19421
https://treeherder.mozilla.org/logviewer?job_id=345301972&repo=autoland&lineNumber=2498

https://hg.mozilla.org/mozilla-central/rev/8c8f5b2f16d3
https://hg.mozilla.org/mozilla-central/rev/5eb0f543b04a
https://hg.mozilla.org/mozilla-central/rev/7a624fe10146
https://hg.mozilla.org/mozilla-central/rev/87cc59582372