Feat/agentflow Port Markdown Editor & Edit/Source Toggle from legacy UI to agentflow (#6125)

* Initial flow

* Fix markdown import shape

* Add support to check for HTML or markdown

* Fix values not being persisted

* Make implementation similar to v2

* Add vairable syntax support to expandDialog

* Add variable syntax support to messageInput

* Test cases added

* Remove eslint-disable

* Add getHtml as a fallback

* Fixed gemini comments

* Fix test cases and lint warnings

* Fixed editorUtils.test to not have nested structure

* Fix review comments