Bug 1723882 [wpt PR 29889] - Fix an element directionality, a=testonly

Automatic update from web-platform-tests
Fix an element directionality

This CL fixes the bugs raised up during the discussion of slots
at whatwg/html#3699.
 - Resolve the light tree element's directionality in the light tree
   and do not walk into the shadow tree for encapsulation.
 - Resolve the element's directionality when there is not a slotted
   node.

Bug: 1236384
Change-Id: Id22aa3e5b624a2e3234c645e198749360f3a050d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3066807
Reviewed-by: Rune Lillesveen <futhark@chromium.org>
Commit-Queue: Miyoung Shin <myid.shin@igalia.com>
Cr-Commit-Position: refs/heads/master@{#909242}

--

wpt-commits: 64bba2c43109cc8a3173ac45d4216fa65624d0bc
wpt-pr: 29889

testing/web-platform/tests/html/dom/elements/global-attributes/dir-slots-directionality.tentative.html

@@ -31,7 +31,7 @@
 test(() => {
   assert_equals(getComputedStyle(host1.firstChild).direction, "rtl");
   assert_equals(getComputedStyle(root2.querySelector("span")).direction, "rtl");
-  assert_equals(getComputedStyle(host3).direction, "rtl");
+  assert_equals(getComputedStyle(host3).direction, "ltr");
   assert_equals(getComputedStyle(root4.querySelector("span")).direction, "rtl");
   assert_equals(getComputedStyle(root5.querySelector("span")).direction, "rtl");
 }, 'Slots: Directionality');