Provide textual content for a given uri.
The editor will use the returned string-content to create a readonly document. Resources allocated should be released when the corresponding document has been closed.
An uri which scheme matches the scheme this provider was registered for.
A cancellation token.
A string or a thenable that resolves to such.
A text document content provider allows to add readonly documents to the editor, such as source from a dll or generated html from md.
Content providers are registered for a uri-scheme. When a uri with that scheme is to be loaded the content provider is asked.