Rename "Kill" to "FakeKill".  Add placeholders for FakeDef and FakeUse.

These are the pseudo-instructions for dealing cleanly with liveness
analysis at the target level, when dealing with multi-dest target
instructions, instructions with additional register side effects, and
preventing instructions with necessary side effects from being
dead-code eliminated.
Move IceInstFakeKill code closer to IceInstTarget.  No functional change.
Add FakeDef and FakeUse class definitions and basic implementation.
Add a FakeUse instruction after a non-intrinsic I32 call.

This prevents the call from being dead-code eliminated.
Fix dump string for the FakeUse instruction.
Replace IceInst::DisallowDead with using IceInstFakeUse.
Use accessor isLastUse() instead of direct LiveRangesEnded[] value.
Clang-format latest round of changes using "make format".