#| highlighting alternative

[vezwork]

Fixes #409

This is an alternative approach to #1084.

This PR is a very simple change: it adds a yaml injection language for #| comments. This means that our syntax highlighting will delegate to the yaml language highlighter inside of #| comments.

The quarto.tmLanguage change is generated from the build-lang.js script.

IMO this is a more "correct" approach, if you will. We lose control over how the yaml looks, but we shouldn't really have that control anyway (let yaml be yaml)?

Pros

• very simple
• uses VSCode's yaml highlighting so it'll match frontmatter (which uses the same injection language approach) and yaml files

Cons

• yaml highlighting is a little visually intense in default themes
• no background colour
• possibly has some weird edge cases? I expected multiline yaml stuff to not work well, but it seems to work just fine. I tried using some yaml-feature-test yaml as a hash pipe comment, and it worked well.

Testing note

We could test that the generated tmLanguage delegates #| properly in some examples, in a non-integrated way, by using vscode-textmate and vscode-oniguruma as dependencies in the tests, but that seems a little heavy handed so I didn't do that.

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