chore: add DataCollection#item, EmptyBlock:type

[johncowen]

Adds an item slot to DataCollection, to be used instead of :find="true"

Previously when using DataCollection:find="true" you then also needed to do items[0] to always refer to the first and only item in the list. Now you can use the #item="{ item }" slot instead of :find="true", eventually we can remove :find entirely.

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Adds EmptyBlock:type and then uses that and makes use of t inside of a reusable component.

DataCollection also has DataCollection:type which is just passed through to EmptyBlock

There is a fair amount of decisions here based on supporting what we currently/used to have, whilst moving forwards with a different approach.

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