filter-menu: Built-in search functionality

[LuLaValva]

Enhancement Request

• Add optional automatic filtering of items in <ebay-filter-menu> via the search header

Description

• For basic use cases, it may be useful for the filter menu to handle searching through items automatically

Note

I'm still not sure this is necessary, for the reasons outlined in #2330:

• There are likely multiple types of custom filtering (i. e. case sensitive, beginning of term vs within term)
• Simple cases that would likely be a good candidate for eBayUI to do the filtering should likely not even have a search filter to begin with
• Network requests are impossible to handle in eBayUI

If this feature will never be used, it is unnecessary bloat for the component

Context

• filter-menu: add search header #2329 added a search header to filter-menu, but all filtering happened externally

Screenshots

[agliga]

we should add this also to listbox-button

[ianmcburnie]

Make sure not to implement this searchbox as role=combobox (i.e. it is not expected to access the items with ARROW keys while focus is on textbox). Keyboard user needs to explicitly tab from textbox to menu.

We'll update the MIND patterns with full guidance.