[css-lists] `counter-reset` should be able to compute to `reversed()` without integer

See https://drafts.csswg.org/css-lists/#propdef-counter-reset

Computed value: the keyword none or a list, each item an identifier or a reversed() function paired with an integer

I think this should be

Computed value: the keyword none or a list, each item an identifier or a reversed() function optionally paired with an integer

Because if you use counter-reset: inherit and the parent had counter-reset: reversed(c), I guess you want to recalculate the start value in the subscope, instead of inheriting the start value of the parent. Thus the start value shouldn't be part of the computed value.

As https://drafts.csswg.org/css-lists/#instantiating-counters says,

When a counter is instantiated without an initial value, the user agent must dynamically calculate the initial value at layout-time to be the number of elements and pseudo-elements that instantiate the same counter in the same scope, plus 1.

So not at computed-value time but at layout-time.

Start with the CSS Lists specification's counter-reset definition and the linked “Instantiating counters” section. Check how computed values and layout-time counter initialization interact for inherited reversed() counters. Done means resolving the proposed optional-integer wording and updating the specification consistently.