vfmt: fix fmt for map value type using select import symbol (fix #20449) (#20451)

vlib/v/fmt/fmt.v

@@ -2629,6 +2629,7 @@ pub fn (mut f Fmt) map_init(node ast.MapInit) {
 			sym := f.table.sym(node.typ)
 			info := sym.info as ast.Map
 			f.mark_types_import_as_used(info.key_type)
+			f.mark_types_import_as_used(info.value_type)
 			f.write(f.table.type_to_str_using_aliases(node.typ, f.mod2alias))
 		}
 		if node.pos.line_nr == node.pos.last_line {

vlib/v/fmt/tests/import_selective_map_keep.vv

@@ -0,0 +1,5 @@
+import time { Duration }
+
+fn main() {
+	println(map[string]Duration{})
+}