types: export helper union types

[filmaj]

Summary

This PR fixes #1818. It exports a bunch of helper unions that we use when authoring these types, but that we've heard from the community that they could possibly want to use themselves in their apps (see #1227).

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 81.76%. Comparing base (1583183) to head (1ba295a).

Additional details and impacted files

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  Coverage   81.76%   81.76%           
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  Files          35       35           
  Lines        7742     7742           
  Branches      316      316           
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  Hits         6330     6330           
  Misses       1400     1400           
  Partials       12       12           

Flag	Coverage Δ
cli-hooks	95.07% <ø> (ø)
cli-test	53.80% <ø> (ø)
oauth	76.51% <ø> (ø)
socket-mode	59.41% <ø> (ø)
web-api	96.53% <ø> (ø)
webhook	95.20% <ø> (ø)

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[zimeg]

Solid improvements as always! Having exposed types for rich text is super helpful, so thank you for typing this 👏

All of these changes look good to me and the JSDoc is awesome 🚀 📚 No blockers but for my own understanding, are we wanting to export types in this granular way in most cases?

[zimeg]

Great to see these ordered and matching the docs 🙌

[filmaj]

are we wanting to export types in this granular way in most cases?

@zimeg Great question; I don't think so, and I would personally default to keeping things internal/non-exported, at least as an initial move, because:

1. It's easier to put something out there than it is to retract; adding something new is additive while taking something away is a breaking change.
2. In terms of TS specifically, it can be harder to know and manage what is unused if we just export everything.
3. In this particular case, we specifically had a request from the community to export this particular type; see this OP in Add Timepicker to @slack/types #1226:

Moving union types to their own exported types. For example, elements supported within the ActionsBlock having a type of ActionsElements. For SectionBlock, SectionElements. Etc.

Of course always open to discussing and changing this inclination if the team feels otherwise.