Fix libui Region::validate() overflow aborts.

This disables the signed integer overflow sanitizer in getWidth,
getHeight, and getBounds. The overflows in these are expected and
benign. Disabling this should fix the aborts we were seeing in
Region::validate(). These functions are inline, so they don't show
up in the stack trace.

Bug: 69963030
Test: Compiles.
Change-Id: I85b43c166339e6c210f7d8f18d1661746efeada7