Splits the preview part of the markdown preview from the dynamic preview management part of things. Static preview swap to preview the active markdown file and don't scroll sync with any other markdown files
For #77131Fixes#93963Fixes#94515Fixes#94517Fixes#94527Fixes#94509Fixes#94514Fixes#93996Fixes#93913
This removes explicit edits from the API and reshapes the API to more closely match VS Code's internal API. The change also tries to better express the lifecycle of backups
For #77131
- Use a class for `CustomDocument` instead of an interface. Extensions can now add their own data to a `CustomDocument` by sublassing
- Renamed `resolveCustomDocument` to `openCustomDocument` and require that extensions return a `CustomDocument`
- Exposed edits on `CustomDocument`
- Made the third parameter of `registerCustomEditorProvider` a generic options bag that takes a `webviewOptions`
For #77131
Going back the the delegate based model for a few reasons:
- It gives us a better approach to add additional API hooks in the future (such as for rename)
- In practive, the capabilities were almost always the same as the `userData` on the document. It is rather confusing to have both `userData` and the capabilities 'on' the document
For #77131
**Motivation**
While our existing webview editor API proposal more or less works, building an editable webview editor is fairly tricky using it! This is especially true for simple text based editors.
It'd also be nice if we could get bi-directional live editing for text files. For example, if I open the same file in a webview editor and in VS Code's normal editor, edits on either side should be reflected in the other. While this can sort of be implemented using the existing API, it has some big limitations
**Overview of changes**
To address these problems, we've decided have two types of webview editors:
- Text based webview editors. These editors used a `TextDocument` as their data model, which considerably simplifies implementing an editable webview. In almost all cases, this should be what you use for text files
- Complex webview editors. This is basically the existing proposed API. This gives extension hooks into all the VS Code events, such as `save`, `undo`, and so on. These should be used for binary files or in very complex text editor cases.
Both editor types now have an explicit model layer based on documents. Text editor use `TextDocument` for this, while custom editors use `WebviewEditorCustomDocument`. This replaces the delegate based approach previously used.
