Fixes #25125

**Bug**
Sometimes the scroll position of webviews is reset. The root cause seems to be rapid edits to the markdown preview resulting in the creation of multiple old content iframes

**Fix**
Only maintain two iframes at most. Ensure that these are properly used when updating

* Preserve Webview Scroll Position

Fixes #22995

**Bug**
If you switch away from an editor that users a webview, the scroll position is currently not preserved. This effects our release notes and the markdown preview. The root cause is that the webview is disposed of when the view is hidden.

**Fix**
Add some presisted state to track scrollProgress through the webview. Use this state in the standard html editor and in the release notes.

* Use view state

* Continue prototype memento based approach

* Preserve Webview Scroll Position

Fixes #22995

**Bug**
If you switch away from an editor that users a webview, the scroll position is currently not preserved. This effects our release notes and the markdown preview. The root cause is that the webview is disposed of when the view is hidden.

**Fix**
Add some presisted state to track scrollProgress through the webview. Use this state in the standard html editor and in the release notes.

* Revert changes to ReleaseNotesInput

Two changes:

* Changes the logic from 41467b74 to make the padding customizable. The default 20px padding is preserved, but now preview can customize if they want to use it or not. This allows html preview page background colors to correctly fill the entire frame.

* Remove Writing the `_defaultStyles` to the root of the webview elment. These are only needed inside of the iFrame itself

Adds enhanced security settings for the markdown preview. The new flow disable all scripts within the preview itself. Users can enable scripts on a per workspace basis.

When a markdown document that uses scripts is loaded, a warning is shown inside the document itself. This warning triggers a new security selector quick pick which allows users to enable or disable enahanced security in the workspace.

**Bug**
Some regression since 1.9 caused the scroll preserve behavior of webviews to stop working in certain cases. There appears to be a race condition where `newFrame.contentDocument.body` does not exist when the scroll update code is called

**Fix**
Instead of using a timeout, update the scroll position when `DOMContentLoaded` is fired from the webview window

Fixes #21491

**Bug**
When refreshing a webview, a slight flicker can sometime be seen. This is especially noticable when using the markdown preview.

**Fix**
Instead of replacing the content of the iframe for refresh, create a new iframe with the new content and do a swap to update.

* Adds command to post a message to an html preview

**Bug**
There is currently no easy way to communicate with an html preview document after the preview has been created.

**Fix**
Adds a command called `vscode.htmlPreview.postMessage` to post a message to a visible html preview. This message will only be posted if the target preview is visible.

Inside the preview, the event is recieved using the standard dom event:

* Remove logging

* proto

Continue proto

* clean up rendering

* Gate prototype

* Fix gating

* Remove public command

* Change setting name

* Added current position indicator

* Reveal center

**Bug**
In the markdown preview, clicking on a page link causes the editor to go blank. This effects our release notes.

**Fix**
Fix the webview pre script which was accidentially slightly changed when it was extracted.

This extracts the JS content from the webview html into its own file which is loaded using preload instead.