Clip to layer bounds when drawing blur regions

Otherwise blurs can "escape" layer bounds. This would make 1-2
pixel-large layers fill the entire screen if the blur region is
appropriately crafted, which is not great.

Bug: 455563813
Flag: EXEMPT CVE_FIX
Test: PoC app
Cherrypick-From: https://googleplex-android-review.googlesource.com/q/commit:123f8fec995a3103acbc3a1191b9cef71523e013
Cherrypick-From: https://googleplex-android-review.googlesource.com/q/commit:ee05b9b41f7579b8fdb18acf674bd86f9f7be2ab
Merged-In: If59833f2d5060f5f81395d602e2dcb369a10fdbb
Change-Id: If59833f2d5060f5f81395d602e2dcb369a10fdbb