Add ".webp" to default compress extensions

The .webp extension contains compressed image data so do not deflate
.webp files in APKs.

Bug: 166137617
Test: aapt2 link
Merged-In: I70181437e0b51122c7aa5047bd0a0791ac3b8df6
Change-Id: I70181437e0b51122c7aa5047bd0a0791ac3b8df6