Add support for multiple font faces

Commits

chore: Fix submodule init check

As far as I can tell, the .git/modules/gitlab-vscode-extension/HEAD file is present even if the submodule hasn't been initialised.

Instead, check for the presence of a file we expect: package.json.

chore: Upgrade @gitlab/fonts

This brings in GitLab Mono as a replacement for JetBrains Mono.

refactor: Extract utils-escape package

These utilities will be used elsewhere in the workspace in the next commit.

feat: Add support for multiple font faces

Addresses #231 (closed).

Screenshots

Note the difference is very suble: pay attention to the italic fonts, particularly the different a and f glyphs.

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