*: replace interface{} with any keyword

Everywhere including examples, external interop APIs, bindings generators
code and in other valuable places. A couple of `interface{}` usages are
intentionally left in the CHANGELOG.md, documentation and tests.

pkg/compiler/return_test.go

@@ -124,7 +124,7 @@ func TestTypeAssertReturn(t *testing.T) {
 	src := `
 		package main
 
-		func foo() interface{} {
+		func foo() any {
 			return 5
 		}