typeahead: Make menu scrollable with up to 50 options.

To increase the number of options available for the user to pick from,
we increase the limit of options shown to 50 for all typeaheads, and
make the menu scrollable. The max height is set to original height of
the composebox typeahead menu, which fit 8 options or to 95% of the
window height, whichever is smaller.

Fixes: #20620.

web/src/custom_profile_fields_ui.ts

@@ -202,7 +202,6 @@ export function initialize_custom_pronouns_type_fields(element_id: string): void
                 type: "input" as const,
             };
             new Typeahead(bootstrap_typeahead_input, {
-                items: 3,
                 helpOnEmptyStrings: true,
                 source() {
                     return commonly_used_pronouns;