Show a warning when showing the rendered markdown diff

[mjbvz]

Our current implementation has some bugs that can hide changes. However even after fixing these, I'm not 100% confident a unexpected change wont sneak through. Best to make users aware of this while also trying to prevent this

[Copilot]

Pull request overview

Adds a user-facing warning when viewing rendered Markdown diffs to reduce the risk of hidden/unnoticed changes in the rendered diff view. This integrates with the Markdown preview lifecycle so the warning appears only when a diff preview is active, and provides a “Don’t Show Again” option.

Changes:

• Introduces a RenderedDiffWarningManager that shows a status bar warning while a rendered diff preview is active and a one-time warning notification.
• Tracks whether a preview is a diff view (isDiffView) and wires active-preview changes in MarkdownPreviewManager to drive the warning UI.
• Minor cleanup in the document renderer (trailing comma + narrow ExtensionContext typing + comment wording update).

Show a summary per file

File	Description
extensions/markdown-language-features/src/preview/renderedDiffWarning.ts	New manager to show status bar + notification warning for rendered markdown diffs, with suppression stored in memento.
extensions/markdown-language-features/src/preview/previewManager.ts	Injects and drives the warning manager based on the active preview and whether it’s a diff view.
extensions/markdown-language-features/src/preview/preview.ts	Adds isDiffView tracking and exposes it through IManagedMarkdownPreview implementations.
extensions/markdown-language-features/src/preview/documentRenderer.ts	Small formatting fix and narrows context type to only extensionUri; updates comment wording.
extensions/markdown-language-features/src/extension.shared.ts	Passes context.workspaceState into MarkdownPreviewManager to back warning suppression/one-time state.

Copilot's findings

• Files reviewed: 5/5 changed files
• Comments generated: 1