`dropdown_search` option for infoj entry edit.options []

[simon-leech]

In multi-filter - we use dropdown_search to allow a user to quickly filter a list by searching.
We should allow this same functionality on an edit.options dropdown list.
If the list is more than about 10 values, it is annoying to manually scan through it to find the value you want.

I propose we add the entry.edit.dropdown_search that would then convert the entry to use search.

I tested this by applying search: entry.edit?.dropdown_search, to line 221 of /locations/entries/text.mjs.
This did convert the dropdown to allow search and selection.

Things that needed to be fixed though:

1. The callback on line 206 sets the newValue to _entry.option which is not returned when dropdown_search is used.
2. The placeholder is set to the current value and not updated when the value is changed.