* theme: fix unthemable icons in several areas
We manually used icon characters in several areas. These are/were entire unthemable. Fixing this required people to manually listen to the theme service and apply rules to their elements when icons change. This PRs adds theme variables that people can use instead.
Fixes#208343
* implement review comments
* fix font-family variable
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Co-authored-by: Martin Aeschlimann <martinae@microsoft.com>
