[dev.typeparams] cmd/compile: fixing case where type arg is an interface
In this case, we can't use an itab for doing a bound call, since we're
converting from an interface to an interface. We do a static or dynamic
type assert in new function assertToBound().
The dynamic type assert in assertToBound() is only needed if a bound is
parameterized. In that case, we must do a dynamic type assert, and
therefore need a dictionary entry for the type bound (see change in
getGfInfo). I'm not sure if we can somehow limit this case, since using
an interface as a type arg AND having the type bound of the type
arg be parameterized is a very unlikely case.
Had to add the TUNION case to parameterizedBy1() (which is only used for
extra checking).
Added a bunch of these test cases to 13.go, which now passes.
Change-Id: Ic22eed637fa879b5bbb46d36b40aaad6f90b9d01
Reviewed-on: https://go-review.googlesource.com/c/go/+/339898
Trust: Dan Scales <danscales@google.com> Reviewed-by: Keith Randall <khr@golang.org>