Specify that value_set's size is compile-time known

[jaehyun1ee]

Following the discussion #1347, this specifies that the size argument of a value_set must be a compile-time known value.

Although the spec already implies it by mentioning:

Parser Value Sets support a size argument to provide hints to the compiler to reserve hardware resources to implement the value set.

This revision makes it more explicit.

[vlstill]

Looks good to me. I can't see a way in which this could be runtime defined.

[jafingerhut]

LGTM

[jafingerhut]

@jonathan-dilorenzo @rcgoodfellow We have two positive reviews on this change, and no verbal objections from LDWG meeting of 2025-Jan-13 from several others. Looks good to us for merging, but leaving it to one of your for final approval/merging.

[jonathan-dilorenzo]

LGTM! Merging, but should this also be mentioned in the compile-time known values section?

[jafingerhut]

LGTM! Merging, but should this also be mentioned in the compile-time known values section?

My belief is that the section on compile-time known values primarily lists what kinds of expression are compile-time known values, but does not attempt to enumerate where such values are required. Where they are required is sprinkled thorughout the document.