[LICM] Hoist loads with invariant.group metadata

Previously loading the vtable used in calling a virtual method in a loop
was not hoisted out of the loop. This fixes that.

canSinkOrHoistInst() itself doesn't check that the load operands are
loop invariant, callers also check that separately.

Reviewed By: rnk

Differential Revision: https://reviews.llvm.org/D99784