AX: Improve CanSetFocusAttribute performance by caching the result.

This patch caches CanSetFocusAttribute result and uses it when needed.

Note that this doesn't follow the typical pattern of updating the cache
because this value can change in response to a new style update,
independently of the ax cache modification count.

Also, this is a fairly heavy function which is not always needed, so
having it be computed in the general cache update can cause a
performance degradation

Perf test results:
test: third_party/blink/perf_tests/accessibility/many-nodes-toggle-content-visibility-auto.html
no patch: 6839ms
patch: 5917ms (-13%)

test: third_party/blink/perf_tests/accessibility/many-nodes-toggle-content-visibility-hidden.html
no patch: 5139ms
patch: 4681ms (-9%)


R=aleventhal@chromium.org, chrishtr@chromium.org

Bug: 1264610
Change-Id: Ie8574ae28baa81d8d2be738560bf0a5a81fdd2bc
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3252717
Commit-Queue: vmpstr <vmpstr@chromium.org>
Reviewed-by: Aaron Leventhal <aleventhal@chromium.org>
Cr-Commit-Position: refs/heads/main@{#937192}