[dev.typeparams] cmd/compile: fix export/import of constants with typeparam type
A constant will have a TYPEPARAM type if it appears in a place where it
must match that typeparam type (e.g. in a binary operation with a
variable of that typeparam type). If so, then we must write out its
actual constant kind as well, so its constant val can be read in
properly during import.
Fixed some export/import tests which were casting some untyped constants
to avoid this problem.
Change-Id: I285ad8f1c8febbe526769c96e6b27acbd23050f0
Reviewed-on: https://go-review.googlesource.com/c/go/+/324189
Run-TryBot: Dan Scales <danscales@google.com>
TryBot-Result: Go Bot <gobot@golang.org> Reviewed-by: Keith Randall <khr@golang.org> Reviewed-by: Cuong Manh Le <cuong.manhle.vn@gmail.com>