Add @vscode/codicons dependency to core package

[msujew]

What it does

Closes #9826

Adds the @vscode/codicons package to the core Theia package. Currently codicons are only available once monaco has been loaded to the DOM. This loads any codicons at startup without the need to include monaco in Theia. I've confirmed that all currently used codicons classes are contained in the referenced css file, except for tree-item-expanded, which I've replaced with chevron-down.

cc @vince-fugnitto does this require a CQ?

How to test

1. Confirm that everything works as expected with this change in place.
2. Modify the example packages to remove any references to monaco packages. See the following dependencies section:

"dependencies": {
    "@theia/bulk-edit": "1.16.0",
    "@theia/callhierarchy": "1.16.0",
    "@theia/core": "1.16.0",
    "@theia/file-search": "1.16.0",
    "@theia/filesystem": "1.16.0",
    "@theia/git": "1.16.0",
    "@theia/keymaps": "1.16.0",
    "@theia/messages": "1.16.0",
    "@theia/metrics": "1.16.0",
    "@theia/mini-browser": "1.16.0",
    "@theia/navigator": "1.16.0",
    "@theia/preferences": "1.16.0",
    "@theia/scm": "1.16.0",
    "@theia/scm-extra": "1.16.0",
    "@theia/workspace": "1.16.0"
},

3. Compile everything and start the application. Confirm that any codicons are correctly rendered. (e.g. chevrons for tree explorers, settings gear in the bottom left corner)

Review checklist

• as an author, I have thoroughly tested my changes and carefully followed the review guidelines

Reminder for reviewers

• as a reviewer, I agree to behave in accordance with the review guidelines

[vince-fugnitto]

cc @vince-fugnitto does this require a CQ?

I don't think so (while we always can to be safe), as in our guide for new dependencies we can do the check ourselves, and I confirmed that the license is "creative commons" which is an approved license.

[linhanyu]

I can approve those change were effective in our electron( Macos / Windows )

[vince-fugnitto]

It looks like we finally ran into the issue where codicons are not available, something we predicted a while ago if monaco was not included :)

• Update VSCode Icons #6115 (comment)

With this change, we should be able to update all icons in the framework to codicons without any worries 👍

[vince-fugnitto]

I confirmed that the change fixes the reported issue 👍