Incorrect search docs for stemming and alternate spelling

[gavynd6]

On the Search settings section (https://statamic.dev/frontend/search#settings), the descriptions for use_stemming and use_alternates don't match reality, and gives the impression of more advanced functionality than is available.

Stemming docs:
use_stemming: Whether to use stemming when searching (e.g. "jumping" matches "jump").

However the code for use_stemming simply calls Str::singular() which only handles converting plurals to singluar, so doesn't work for "jumping" to "jump" (which would actually be stemming).

Alternates docs:
use_alternates: Whether to use alternate spellings when searching (e.g. "color" matches "colour").

The code only supports "and" to "&" (or vice versa), or different versions of apostrophes. It doesn't look for alternate spellings at all.