[css-inline-3][css-page-3][css-text] Enforce non-negative value from …

[cdoublev]

Adds [0,∞] to CSS types in contexts that require a non-negative value.

[frivoal]

Looks fine to me, and it's OK IPR-wise, as this is an editorial change.
@fantasai, as editor of css-inline and css-page, can you confirm this is fine by you?

[cdoublev]

Please let me know if you think it is ok to add [1,∞] to fixed <integer>? in system for @counter-style. The integer defines the first symbol value in the list of symbols.

This is not defined in prose, whereas this PR only includes range additions ([0,∞]) that are already defined in prose for now.

edit: nevermind, it may be usefull to specify fixed -1 to set the last symbol as the first symbol value.