Add stack trace logging when EG test helper fails to find element

Prints the call stack trace to help debug the endlessly spinning
GridCell MDCActivityIndicator [ChromeEarlGrey
waitForUIElementToAppearWithMatcher:timeout:]

Bug: 1352968, 1352970
Change-Id: I75d22cc280270828461b6d853698abc673bbde40
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3863344


Reviewed-by: Rohit Rao <rohitrao@chromium.org>
Auto-Submit: Mike Dougherty <michaeldo@chromium.org>
Commit-Queue: Rohit Rao <rohitrao@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1042258}