Add TailDecoration comma as content rather than CSS

[colin-grant-work]

What it does

Modifies the approach taken to adding a comma between tail decorations to put it in the HTML markup rather than the CSS.

How to test

1. Open a file and create some problems, then save it.
2. See something like this in the navigator, with a comma:
   
3. Install GitLens, open the Branches tree view, and select one of the branches.
4. See this:
   

Not this (note funny commas):

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]

I confirm that the changes work well 👍