feat(pickers): allow the scrolling limit to be configured

[davvid]

Promote the "temp__scrolling_limit" option into an officially supported
configuration field that controls the number of results displayed by pickers.

Closes: #2779

[alerque]

Should this option be documented somewhere?

[davvid]

@alerque thanks for considering this enhancement. I rebased and added a commit that documents this option. Let me know if there's a better place to document it.

BTW, from re-reading the code, it could be argued that max_results would be a better name for this option. max_results is the same name as the actual self.max_results field that opts.scrolling_limit gets assigned to, so it might be clearer to name them consistently.

I can add another commit to rename the field if this is being considered for merging and you agree that it's worth changing that detail. The current name came from removing the temp__ prefix from the original variable's name. I didn't think about it too much at the time. cheers