v1.6: Restore ability for programs to upgrade themselves (#20263)

* Make helper associated fn

* Add feature definition

* Restore program-id write lock when upgradeable loader is present; restore bpf upgrade-self test

* Remove spurious comment

cli-output/src/display.rs

@@ -140,7 +140,7 @@ fn format_account_mode(message: &Message, index: usize) -> String {
         } else {
             "-"
         },
-        if message.is_writable(index) {
+        if message.is_writable(index, /* restore_write_lock_when_upgradeable=*/ true) {
             "w" // comment for consistent rust fmt (no joking; lol)
         } else {
             "-"