feat: add custom filtering option to combobox

[simonxabris]

🙋 Feature Request

I'd like to be able apply my custom filtering logic when using the combobox in an ergonomic manner.

💁 Possible Solution

My idea is that a customFilter property could be added to the Combobox class that users can bind a function to with (roughly) the following signature: (option: ListboxOption) => boolean. This function would define if an option fits the given criteria or not and then pass this in to this filter here: https://github.com/microsoft/fast/blob/cae5b3fab883ce38f623192ba9d7a8b105208cd2/packages/web-components/fast-foundation/src/combobox/combobox.ts#L320-L322

🔦 Context

This would make the combobox much more flexible to use in my opinion, in our org this need comes up very frequently.

[atmgrifter00]

+1 for such a feature! I started a Discord discussion about this very thing not long after this issue was created.