Fixes#72155
Adds a constant to the api that tracks the root path for resources inside of webviews. This is required because we will not be able to use `vscode-resource:` uris on the web. Our current approach is to rewrite the html we are given but there are almost certainly going to be cases where we don't get this quite right.
Adopts the new api for the markdown preview
* Add WebviewPanel.iconPath
Allows webviews to provide icons used in UI. Adds a new `WebviewPanel.iconPath` property for this.
Replaces the static contribution approach from #49657Fixes#48864
* Fix doc
* Move icon into mainthreadwebview
* Cleaning up implementation
* Cleaning up implementation