Icon Picker: Filter icons in modal

[bjarnef]

Prerequisites

• I have added steps to test this contribution in the description below

If there's an existing issue for this PR then this fixes part of #20632 and part of #20647

Description

[github-actions]

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[nielslyngsoe]

Hi @bjarnef

Great to see you taking action on this one.

I will have to say, from a Seperation Of Concerns perspective, I would like the Icon Picker Modal to be as little knowledgeable of the implementation as posible.

So ideally, to align with other Pickers, the filter going into the modal would be a method that takes the whole model for Icons. So defined like this:

filter?: (item: UmbIconDefinition) => boolean;.

In this way the Icon Picker implementation can run the logic of its choice.
— Like I dream that we one day have keywords as part of the Icon model, and categories, and this filtering methods could be used for that as well. :-) I hope that makes sense, thanks

[bjarnef]

@nielslyngsoe great suggestion and I was looking with a possible type for regex, there's a RegExp, but no type for pattern although there are suggestions here: microsoft/TypeScript#41160

In custom code of we can control filter for the modal and possible later passed in as config to property editor #20632

But in core icon picker, I think we should consider this as well. In this case I don't want my custom registered icons to show up in icon picker for content types and some may register icons used for custom features in e.g. a dashboard, while it may not make sense this appear in icon picker.