System functions: Make sure all pages, including disambiguation pages, have at least one example

Some pages, like language-reference-guide/docs/system-functions/class-disambiguation.md have no examples. There should be one (ideally short) example for each of the monadic and dyadic forms.

Also ensure that pages that have now been split all have at least one example, i.e. that it isn't the case that all the examples were inherited by one valence.

In some cases, the monadic form is equivalent to the dyadic form with a default left argument. In those cases, simply extract the examples that use the default value and use those.

In some cases, the dyadic form with a certain left argument is equivalent to the monadic form. In those cases, simply extract the monadic form and add the otherwise implied left argument.

Start by reading language-reference-guide/docs/system-functions/class-disambiguation.md and surveying the other system-function pages, especially pages that were split by valence. Check each monadic and dyadic form for at least one short example, reusing equivalent default-argument examples where applicable. Done means no relevant page or form is left without an example and split pages do not leave all examples on only one valence.

Written by the indexing model from the issue text.