Fixes #47621

Adds the concept of a source code action that applies to an entire file. Does not show these actions in the lightbulb menu by default

* Split out `Webview` from `WebviewEditor` in API

**Problem**
The current proposed `Webview` interface has a few methods and properties that are very editor specific, such as `.reveal` and `.onDidChangeViewState`. These properies will not make sense if we ever allow webview to be displayed in other locations, such as in widgets

**Proposal**
Split the concepts of a `Webview` and of a `WebveiwEditor`. A webview is the html content itself. A `WebviewEditor` is an editor that displays a `Webview`

This would allow us to easily add other types of `Webview` owning objects in the future without having to document that some methods only apply when a webview is used as an editor vs as a widget

Fixes #47634