This primarily implements DecorationImage.lerp().

It also makes some minor tweaks, the main one of which is defering to dart:ui for `clampDouble` instead of duplicating it in package:foundation.

Fixes https://github.com/flutter/flutter/issues/12452

This was first landed in https://github.com/flutter/flutter/pull/130533 and reverted in https://github.com/flutter/flutter/pull/131347.