[a11y-android] Add ignored checking to isNodeValid.

TalkBack can attempt to query or manipulate nodes that are marked as
ignored (for example, when traversing stale caches or layout relations).
Performing operations such as populating node info or setting selections
on ignored nodes can cause crashes when computing text offsets, querying
child counts, or asserting node boundaries.

This change adds checking `!IsIgnored()` to `IsNodeValid` function.

Cq-Include-Trybots: luci.chromium.try:android-16-x64-rel
Bug: 545549814
Change-Id: Ib8eb943d150753621859b697dbae98742980ad7f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/8256250
Commit-Queue: Ramin Halavati <rhalavati@chromium.org>
Auto-Submit: Ramin Halavati <rhalavati@chromium.org>
Reviewed-by: David Tseng <dtseng@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1679462}