Optimizing: Fix TypeConversion(And(x, const)) simplification.

Avoid introducing implicit conversions when simplifying the
expression TypeConversion(And(x, const)). Previously, when
we dropped the And, we could end up with a TypeConversion to
the same type which should be eliminated on subsequent pass
of the block's instructions; however, a subsequent dependent
TypeConversion in the same block would be processed earlier
and we would unexpectedly see its input as the conversion to
the same type, failing a DCHECK().

Bug: 27626509
Change-Id: I5874a9ceafbf635cf3391beea807ede8468ab5c3