Backed enum value changed to Atomic instead of scalar int or strings

[tuqqu]

Closes #9938

[weirdan]

Since there are no BC breaks, you can target 5.x instead of master.

[tuqqu]

@weirdan the target branch is changed

[weirdan]

the target branch is changed

On second thought, the following would break:

fn(EnumCaseStorage $s): int|string|null { return $s->value; }

It looks like I relied on automated checks too much. I've changed the target branch back to master, sorry about this confusion.

[weirdan]

Suggested change

	if ($enum_case_storage->value instanceof TLiteralString
	|| $enum_case_storage->value instanceof TLiteralInt) {
	if ($enum_case_storage->value !== null) {

[weirdan]

Thanks!