use clipping in the recent commit to actually test bounding boxes
added a void contract to fix setup
Cleanup kw/opt lambda annotations.
Make kw/opt lambda special checks work with other expected values.

Closes PR13544.
Reduce unnecessarily complicated restrict case.
Fix type of split-at and vector-split-at.

Closes PR12700.
Reduce usage of check-below.

This pushes almost all uses of check below into tc-expr and
tc-expr/check. This means that the optimizer sees more precise types
and can make more optimizations.
Fix issues from bad merge.