markused: keep str_intp for aliases whose codegen wraps parent str()

When a `type Foo = Bar` alias has no str method of its own but its parent
type does, cgen emits a wrapper `indent_Foo_str` that calls
`builtin__str_intp` to format `'Foo(...)'` around the parent's str output
(auto_str_methods.v gen_str_for_alias). type_auto_str_needs_str_intp was
unaliasing first and seeing the parent's str method, so it returned false
and -skip-unused dropped str_intp / StrIntpData, producing `implicit
declaration of function 'builtin__str_intp'` for any program that just
calls .str() on an SDL Version (and other c2v-style aliases).

Check the pre-unaliased sym for the Alias-without-own-str case before
falling through to the unaliased-parent-has-str shortcut.

Author: medvednikov

vlib/v/markused/walker.v

@@ -2842,6 +2842,10 @@ fn (mut w Walker) type_auto_str_needs_str_intp(typ ast.Type) bool {
 	if resolved_typ.is_ptr() || resolved_typ.is_pointer() {
 		return true
 	}
+	raw_sym := w.table.sym(resolved_typ)
+	if raw_sym.info is ast.Alias && !raw_sym.has_method('str') {
+		return true
+	}
 	sym := w.table.final_sym(w.table.unaliased_type(resolved_typ))
 	if sym.has_method('str') {
 		return false