[mediaqueries] Merge error handling section into evaluating section

At this point, it's not clear what the motivation to have https://andreubotella.com/csswg-auto-build/mediaqueries-4/#error-handling as a separate section to https://andreubotella.com/csswg-auto-build/mediaqueries-4/#evaluating is.

The current split leads to some ambiguities in places:

An unknown <media-type> must be treated as not matching.

What does "not matching" mean, given "a media query is a logical expression that is either true or false"? (This also runs into #7594 given we don't define how to evaluate <media-type>.)

An unknown <mf-name> or <mf-value>, or a feature value which does not matches the value syntax for that media feature, results in the value “unknown”.

Results in the value "unknown" for what? Does it make the <media-feature> unknown, or the closest parent <media-condition> unknown, or does it make the whole <media-query> unknown? Implementations currently differ here!

A <media-query> whose value is “unknown” must be replaced with not all.

But, as above, a media query is either true or false? What does it mean to "replace" a <media-query>?

It seems like we may well want to define the rewriting to not all in Serializing Media Queries instead?

Read the Media Queries 4 “Error Handling” and “Evaluating” sections, including the cited examples for unknown media types and features. Compare the proposed handling with CSSOM’s “Serializing Media Queries” section and issue #7594; done means the relevant behavior and terminology are defined consistently, including where rewriting to not all belongs.