[dev.typeparams] cmd/compile: fix use of method values with stenciled methods
We were handling the case where an OFUNCINST node was used as a function
value, but not the case when an OFUNCINST node was used as a method
value. In the case of a method value, we need to create a new selector
expression that references the newly stenciled method.
To make this work, also needed small fix to noder2 code to properly set the
Sel of a method SelectorExpr (should be just the base method name, not
the full method name including the type string). This has to be correct,
so that the function created by MethodValueWrapper() can be typechecked
successfully.
Fixes #45817
Change-Id: I7343e8a0d35fc46b44dfe4d45b77997ba6c8733e
Reviewed-on: https://go-review.googlesource.com/c/go/+/319589 Reviewed-by: Keith Randall <khr@golang.org>
Trust: Dan Scales <danscales@google.com>