[LS] Format docstring annotations

[turbolent]

Description

Pre-process docstrings before displaying them in hover and completion results. Parse the annotations as supported in the documentation generation tool, converting @param name: desc and @return desc annotations into readable Markdown.

Parameters are rendered as a **Parameters** section with a bulleted list (- `name`: desc), return values as **Returns** desc, both placed at the end after any other content.

Docstrings are pre-processed in all three places where they are surfaced: hover, member completion resolution, and range completion resolution.

Reported by @holyfuchs in onflow/flow-credit-markets#10 (comment)

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• 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