bug#22147: Obsolete search-forward-lax-whitespace

[Juri Linkov]

> IIUC, Drew was offering an implementation of symmetric char folding,
> whereas the release blocking aspect of this bug is to add a
> char-folding-ad-hoc variable.

My initial request was to restore an ability to fold whitespace.
One way to do this is to implement symmetric char folding.
However, I believe that the same could be achieved with just
char-fold-ad-hoc providing a suitable set of mappings.  I'll confirm
whether this is achievable after adding char-fold-ad-hoc.