cmd/compile: allow delaying of transformCompLit, new transformAddr

For this unusual case, where a constraint specifies exactly one type, we
can have a COMPLIT expression with a type that is/has typeparams.

Therefore, we add code to delay transformCompLit for generic functions.
We also need to break out transformAddr (which corresponds to tcAddr),
and added code for delaying it as well. Also, we now need to export
generic functions containing untransformed OCOMPLIT and OKEY nodes, so
added support for that in iexport.go/iimport.go. Untransformed OKEY
nodes include an ir.Ident/ONONAME which we can now export.

Had to adjust some code/asserts in transformCompLit(), since we may now
be transforming an OCOMPLIT from an imported generic function (i.e. from
a non-local package).

Fixes #48537

Change-Id: I09e1b3bd08b4e013c0b098b8a25d082efa1fef51
Reviewed-on: https://go-review.googlesource.com/c/go/+/354354


Run-TryBot: Dan Scales <danscales@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Trust: Dan Scales <danscales@google.com>
Reviewed-by: Keith Randall <khr@golang.org>