[ValueTracking] Update implied reasoning to accept expanded cmp (NFC).

This patch adds versions of isImpliedCondition and
isImpliedByDomCondition that take a predicate, LHS and RHS operands as
instead of a Value representing the condition.

This allows using those functions to check conditions without having a
concrete ICmp instruction.

Reviewers: nikic, RKSimon, lebedev.ri, spatel

Reviewed By: nikic

Differential Revision: https://reviews.llvm.org/D74065