[css-font-4][editorial] Fix <'font'> syntax, simplify <font-variant-css2> and <font-width-css3> syntaxes

[lahmatiy]

According to the CSS Values and Units specification as stated:

If the property’s value grammar is a comma-separated repetition, the corresponding type does not include the top-level comma-separated list multiplier. (E.g. if a property named pairing is defined as [ <custom-ident> <integer>? ]#, then <'pairing'> is equivalent to [ <custom-ident> <integer>? ], not [ <custom-ident> <integer>? ]#.)

The definition of <'font-family'> is [ <family-name> | <generic-family> ]#. When used in the context of <'font'> without the #-multiplier, this implies that only a single <family-name> or <generic-family> can be used as the <'font-family'> value. However, the <'font'> property allows a comma-separated list of family names, which necessitates the explicit inclusion of the #-multiplier with <'font-family'> in the <'font'> syntax.

Additionally, the brackets are redundant in the syntaxes for <font-variant-css2> and <font-width-css3>.

Note: I made changes only to font-4, as font-3 appears to be generated from an external source, and I couldn't locate the source.

[w3cbot]

lahmatiy marked as non substantive for IPR from ash-nazg.