feat: show line numbers in markdown blocks

[Sdju]

Add line numbers for code blocks in Slidev VSCode extension

Motivation

I have many code blocks in my presentations. And I often need to know line numbers (e.g., for line highlighting {1|7-9...} ). It would therefore be useful to see line numbers directly in the editor.

Description

This PR adds an optional feature to display line numbers for code blocks in the Slidev VSCode extension, making it easier to reference specific lines when working with code in presentations.

Screenshots

Changes

1. Line numbers decoration for code blocks

• Added automatic line numbering for code blocks (triple backticks ```)
• Ignores special blocks like magic-move (4+ backticks)
• Added slidev.annotations-line-numbers setting (default: true)

Known issues

1. Doesn't respect the startLine option
2. Shares the same triggers for creating annotations — looks odd until the document is saved
   [Fixed]

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commit: 387fdbd

[antfu]

Love the idea!

[kermanx]

LGTM. The lint error seems to require manual update. About the odd behavior when the document is not saved yet, I wasn't noticing this because I always have autoSave on🥲. Maybe it should be fixed somehow later.

[Sdju]

The lint error seems to require manual update.

Fixed

[kermanx]

LGTM. However, we aren't able to release it before #2207, which is still blocked by upstream.

[ragavkumarv]

Very useful and pragmatic feature. Thanks for doing this ❤️.