fix: add typescript definitions

[SimonChaumet]

Summary

This pull requests adds typescript definitions
Closes #3994

What are the specific steps to test this change?

• check typescript type inference and compile

What kind of change does this PR introduce?

(Check at least one)

• Bug fix
• [ x] New feature
• Refactor
• [ x] Documentation
• [x ] Build-related changes
• Other

Make sure the PR fulfills these requirements:

• [ x] It includes a) the existing issue ID being resolved, b) a convincing reason for adding this feature, or c) a clear description of the bug it resolves
• The changelog is updated
• Related documentation has been updated
• Related tests have been updated

[boutell]

I don't think we would accept a PR to add typings to Apostrophe 2.x because it is late in the Apostrophe 2.x life cycle. New development like this is more appropriate to Apostrophe 3.x.

I'm going to close this initial PR because it is on 2.x but this doesn't mean we're not interested in continuing this conversation about 3.x.

[SimonChaumet]

Our project is still in 2.x and this feature will not create breaking changes or developments from your team

[boutell]

I see. I appreciate the contribution. I am still inclined to think it is too much effort being invested in a version of Apostrophe that will be supported for some time yet but is not the primary focus. To really make this work well and make it possible to type-check, for instance, overridden methods in a piece type module, it would be necessary to make changes to A2 core which is unlikely at this stage. So I would suggest that migration to A3 would be a much more valuable project to pursue first.

(If you work with or for one of our enterprise clients, please do open support tickets within that project so we understand the urgency for the customer and can have this discussion with all the stakeholders concerned.)