android: Use raw strings for stack.py re.compile

Bug: None
Change-Id: I8d0f7ee2dc61e1f4a2c8dbf8b964d0e0eb530051
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6297553
Auto-Submit: Peter Wen <wnwen@chromium.org>
Commit-Queue: Mohamed Heikal <mheikal@chromium.org>
Commit-Queue: Peter Wen <wnwen@chromium.org>
Reviewed-by: Mohamed Heikal <mheikal@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1424135}
NOKEYCHECK=True
GitOrigin-RevId: 5dc5396406c202ae8f7a9b60cf74f3c45672924c