[anchor] Add try-tactics set to the cascade

Similarly to what we do for the regular try set, this CL adds
a CSSPropertyValueSet to OutOfFlowData (the try-tactics set),
which is read during rule collection, and added to the match result
with is_try_tactics_style=true.

For now this is only used by tests. In the future,
StyleEngine::UpdateStyleForOutOfFlow will be responsible
for managing this set (which will ultimately come from out-of-flow
layout).

Bug: 40279608
Change-Id: I8a199c7a311941bcaab5091f374504edc68dfe40
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5349527
Commit-Queue: Anders Hartvoll Ruud <andruud@chromium.org>
Reviewed-by: Rune Lillesveen <futhark@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1270286}