wrapperutils: Cache resolve() results [performance]

At least in the cases that would have called into resolve_impl.

This eliminates a large CPU bottleneck and is reflected in reduced gnome-shell render times:

Animation	Before (average/peak)	After (average/peak)
Icon spring	12ms / 350ms	7ms / 133ms
Window overview	5ms / 10ms	4ms / 7ms

Closes: #302 (closed)