x/tools/go/ssa/interp: allow more string conversions of byte slices

[timothy-king]

We are probably going to accepted more kinds of conversions from byte or rune slices to strings #23536 (comment) .

interp does not currently accept such conversions:

package main

func main() {
	type MyByte byte
	type MyRune rune

	var y []MyByte
	_ = string(y)

	var z []MyRune
	_ = string(z)
}

On the above example ssa/interp will panic with the message:

Panicking: *runtime.TypeAssertionError interface conversion: types.Type is *types.Named, not *types.Basic.

[gopherbot]

Change https://go.dev/cl/501301 mentions this issue: go/ssa/interp: support conversions to slices of named bytes