Support for value-of<MyEnum>

[MidnightDesign]

Psalm doesn't support backed enums as a type argument for value-of:

enum ReservationState: string {
    case Pending = 'pending';
    case Confirmed = 'confirmed';
    case Cancelled = 'cancelled';
}

/**
 * @param value-of<ReservationState> $value
 */
function makeState(string $value): ReservationState {
    return ReservationState::from($value);
}

makeState(ReservationState::Pending->value); // Works
makeState('confirmed'); // Works
makeState('foo'); // Doesn't work

https://psalm.dev/r/1277567ae5

Expected:
No errors

Actual:
ERROR: InvalidDocblock - 10:11 - Untemplated value-of param ReservationState should be an array in docblock for makeState

PHPStan supports this use of value-of.

(I've searched the existing issues for this, but surprisingly, I couldn't find one. I'm sorry if I've missed it.)

[psalm-github-bot]

I found these snippets:

https://psalm.dev/r/1277567ae5

<?php

enum ReservationState: string {
    case Pending = 'pending';
    case Confirmed = 'confirmed';
    case Cancelled = 'cancelled';
}

/**
 * @param value-of<ReservationState> $value
 */
function makeState(string $value): ReservationState {
    return ReservationState::from($value);
}

makeState(ReservationState::Pending->value); // Works
makeState('confirmed'); // Works
makeState('foo'); // Doesn't work

Psalm output (using commit b5b5c20):

ERROR: InvalidDocblock - 10:11 - Untemplated value-of param ReservationState should be an array in docblock for makeState

[AndrolGenhald]

Fixed by #8283.