Improvements to mappings and automate manual steps

Right now adding/changing icons in VS Code feels like it needs too many manual steps.

Issues:

• icons.ttf causes unresolvable conflicts and blocks having multiple PRs open in progress. It should probably not be kept in the git repo being a binary file.
• Can't easily see what icons share a mapping in mapping.json
• Need to manually add an arbitrary number to mapping.json` and its hex value to codicons.ts which is error prone
• icons.ttf needs to be manually committed to the main vscode repo

Possible improvements:

• Add CI to check for errors
• When a PR is merged or a commit made, CI can publish dist/icons.* to the Releases page. This way we keep the repo free of conflicts and can have multiple ongoing PRs open at the same time
• Add icons.ttf to the gitignore so it doesn't get committed.
• Use JSON lists to group names in mapping.json. This way we can see which icon names map to the same icon, and we don't need to add numbers. This will also make the mappings much easier to edit.
• Remove the manual numbering in the mapping.json. This can be autogenerated when the previous suggestion is implemented.
• Automatically create a PR to the vscode repo with the new icons.ttf
• Automatically update vscode-docs

MAGIC LEVEL:

• Launch a web instance for each with the new icons for review.

We can ask Lee to help us with this.
cc @daviddossett

Start by tracing the current workflow around mapping.json, codicons.ts, icons.ttf, and the generated dist/icons.* files. Review how changes are committed to the VS Code repository and how vscode-docs is updated; the issue is complete only when the agreed automation and validation steps replace the relevant manual work.