[ValueTracking] Add tests for additional `isKnownNonZero` cases; NFC

Add cases for the following ops:
    - 0-X
    - bitreverse(X)
    - bswap(X)
    - ctpop(X)
    - abs(X)
    - uadd_sat(X, Y)

Reviewed By: nikic

Differential Revision: https://reviews.llvm.org/D142827