When a template action is created, any (non-meta) instruction operand
will refer to instructions in the corresponding generic, or possibly to
a constant. This means that when the action is eventually executed when
forming a specific, it would see the generic value for that operand
rather than the intended specific value.
Fix this by refining `InstId` operands to refer to a corresponding value
in the specific, much like we would when rebuilding a constant in the
eval block.
Richard Smith
c41033c315