[KnownBits] Define and use intersectWith and unionWith

[KnownBits] Define and use intersectWith and unionWith

Define intersectWith and unionWith as two complementary ways of
combining KnownBits. The names are chosen for consistency with
ConstantRange.

Deprecate commonBits as a synonym for intersectWith.

Differential Revision: https://reviews.llvm.org/D150443