fix(gnolang): fix panic when using struct as index of map (#2044)

Closes #2041. Use fieldlist to get field type
<!-- please provide a detailed description of the changes made in this
pull request. -->

<details><summary>Contributors' checklist...</summary>

- [ ] Added new tests, or not needed, or not feasible
- [ ] Provided an example (e.g. screenshot) to aid review or the PR is
self-explanatory
- [ ] Updated the official documentation or not needed
- [ ] No breaking changes were made, or a `BREAKING CHANGE: xxx` message
was included in the description
- [ ] Added references to related issues and PRs
- [ ] Provided any useful hints for running manual tests
- [ ] Added new benchmarks to [generated
graphs](https://gnoland.github.io/benchmarks), if any. More info
[here](https://github.com/gnolang/gno/blob/master/.benchmarks/README.md).
</details>

gnovm/pkg/gnolang/values.go

@@ -1543,8 +1543,7 @@ func (tv *TypedValue) ComputeMapKey(store Store, omitType bool) MapKey {
 		bz = append(bz, '{')
 		for i := 0; i < sl; i++ {
 			fv := fillValueTV(store, &sv.Fields[i])
-			ft := bt.Fields[i]
-			omitTypes := ft.Elem().Kind() != InterfaceKind
+			omitTypes := bt.Fields[i].Type.Kind() != InterfaceKind
 			bz = append(bz, fv.ComputeMapKey(store, omitTypes)...)
 			if i != sl-1 {
 				bz = append(bz, ',')

gnovm/tests/files/struct58.gno

@@ -0,0 +1,23 @@
+package main
+
+type I interface {
+	dummy()
+}
+type IS struct{}
+
+func (iss IS) dummy() {
+}
+
+type S struct {
+	x int
+	I
+}
+
+func main() {
+	m := make(map[S]string)
+	m[S{0, IS{}}] = "test"
+	println(m)
+}
+
+// Output:
+// map{(struct{(0 int),(struct{} main.IS)} main.S):("test" string)}