Enable DocumentSymbol capability for Outline

[MaxStalker]

Closes #665

Description

• enable DocumentSymbol capability on Language Server to return items for Outline panel in VS Code (and other editors)
• add WithDocumentSymbol method to assign provider to server
• create DocumentSymbol provider to collect DocumentSymbols
• create convertors for AST kind to DocumentSymbol kind

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For contributor use:

• Targeted PR against master branch
• Linked to Github issue with discussion and accepted design OR link to spec that describes this work
• Code follows the standards mentioned here
• Updated relevant documentation
• Re-reviewed Files changed in the Github PR explorer
• Added appropriate labels

[turbolent]

@MaxStalker This is awesome! What is left to be done for this PR to get merged?

If you think it's ready please mark it as ready for review and I'll have a look!

[MaxStalker]

@MaxStalker This is awesome! What is left to be done for this PR to get merged?

If you think it's ready please mark it as ready for review and I'll have a look!

When used with transaction template it would break language server.
I had no chance to look into it yet - that's why this PR is stalled.

[turbolent]

@MaxStalker I spend some time this afternoon to finish this and opened a PR in #943. Do you want to sync on how we could get the PRs merged? I'd love to get this in! 🙂

[turbolent]

Rebased and applied the commits from the follow-up PR

[turbolent]

Great work!

[codecov-commenter]

Codecov Report

Merging #662 (8971510) into master (159015d) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #662   +/-   ##
=======================================
  Coverage   74.20%   74.20%           
=======================================
  Files         267      267           
  Lines       33001    33001           
=======================================
  Hits        24487    24487           
  Misses       7386     7386           
  Partials     1128     1128           

Flag	Coverage Δ
unittests	74.20% <ø> (ø)

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