Suggestion improvements (2)

This PR proposes further improvements, new hooks, and some fixes to the suggestions infrastructure. Depends on (and includes) #108.

st/core: dispatch gathering of completion suggestions to `containingArtefact` for specialization (ab393e3)

For instance, sonyx overrides some of these new 'artefactCompletion' hooks in order to minimize the selector list, add custom selectors, or insert instances from a subclass of SBSuggestionItem.

Video (🔊):

https://user-images.githubusercontent.com/38782922/156855690-2aef301b-2bc3-44f7-9165-c481846569e3.mp4

Open issues on this change:

[ ] Test thoroughly. There might be use cases of the suggestions I am not aware of and thus might have broken. Especially, please check the experience for ordering and availability of suggestions depending on their length vs. typographic distance (fuzzy matching) vs. semantic distance (type guessing).
[ ] Maybe we should even have real acceptance tests for this to make sure that all relevant use cases are covered?
[ ] Discuss the right place for the dispatching hooks. Currently, the collection of completions and suggestions is delegated to the containingArtefact, making it possible for other projects (like sonyx) to subclass SBStContainer. However, this is not necessarily the single truth. Maybe alternatively/additionally dispatch the creation via the editor, the grammar handler, or a completely new entity?

st/core: provide hook `Class>>#sandblocksMetaSuggestionsFor:` (5f84560)

For instance, you could override the hook like this on Color to prioritize color names:

sandblocksMetaSuggestionsFor: aBlock

    ^ self colorNames, (super sandblocksMetaSuggestionsFor: aBlock)

Sonyx makes use of this hook, too.

misc

recategorizations (0d51099)
st: reassure that return expressions can be print-itted (d0d80f9)
core: fix SBSuggestionMenu>>#sandblockEditor (544932d)

The menu is not a sub*morph of the editor, so we need to use the instvar here.
core: fix dismissal of suggestions menu via click if #suggestAlways is true (ac89fb4)

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hpi-swa / sandblocks