Bug 1876401 [wpt PR 44178] - Add tests for direction and bidi isolati…

…on behavior of <slot> element., a=testonly

Automatic update from web-platform-tests
Add tests for direction and bidi isolation behavior of <slot> element.

These tests are based on the tests previously in
https://crrev.com/c/4800075 and https://crrev.com/c/4973701, but are
revised to reflect that the HTML spec changes that those changes were
implementing have been reverted in
whatwg/html#9880

Bug: 576815
Change-Id: Id4536cb39691c2d234113f891f96d7100c7eeea4
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5233352
Reviewed-by: Di Zhang <dizhanggchromium.org>
Auto-Submit: David Baron <dbaronchromium.org>
Commit-Queue: Di Zhang <dizhanggchromium.org>
Cr-Commit-Position: refs/heads/main{#1251783}

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wpt-commits: 41bbcfcc813d99401ca0cacfa392c87d6f18ffca
wpt-pr: 44178

UltraBlame original commit: 6dc79c28daa8bf6d48215692303e1097aa118baa