[css-values-4] Make mod/rem/log return a consistent type

[cdoublev]

About mod(), rem(), random() (fixed in f587be0):

The argument calculations can resolve to any <number>, <dimension>, or <percentage>, but must have the same type, or else the function is invalid [...]

I think "same type" is ambiguous.

For example, with mod(1px, 1%) matching a <length-percentage>, what should it be?

The type of both argument calculations is [length → 1] but 1% also has a length percent hint. The type of mod() should be [length → 1] with a length percent hint, which corresponds to the consistent type.

The type definition of log() is slightly less ambiguous: "<number> made consistent with the input calculation's type". What is the input calculation's type?

Since argument calculations are restricted to <number>s, returning <number> made consistent with each calculation type, or the consistent type is equivalent. If prefer the latter, for consistency.