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
Fixes#60374
Some markdown-it extensions end up reprocessing the same tokens multiple times. This can result in our link normalized being re-invoked on a link, which causes it to fail
Fix to to make sure that `vscode-resource` is a recongized link so that we don't try re-normalizing in these cases
Fixes#58566
We only support local file links or a small set of normal schemes, like `http` and `mailto`. Use this to avoid calling `Uri.parse` with scheme-less paths such as `Uri.parse('/images/cat.gif')`
