Unimplemented pinned datatips and modifier providers

In [the types for `atom-ide-datatip`](https://github.com/atom-community/atom-ide-base/blob/master/types-packages/datatip.d.ts#L5:L6), there are two unimplemented concepts:
- a pinned datatip (presumably, a datatip that stays at a particular position in the editor until dismissed manually)
- a modifier provider (presumably, a provider that is also passed the information about the held modifier keys like Ctrl or Shift)

What would be the use cases for these? So far I don't see much reason to have them. They aren't implemented by the LSP, so it's unlikely that we'll have proper language support for these either.

Start with types-packages/datatip.d.ts lines 5-6 and inspect how atom-ide-datatip represents the two unimplemented concepts. Check the referenced LSP limitations and existing issue discussion for concrete use cases. Done would require a decided scope for pinned datatips and modifier providers, but the issue does not specify an implementation target.

Written by the indexing model from the issue text.