Backport #1097, #1104, #1148

[mergify]

PR Type

What kind of change does this PR introduce?

• Build or CI-related changes
• Documentation content changes

Description

• Include .markdownlint.json and cspell.json as part of the documentation
• Removing <iframe /> for the youtube videos and use proper markdown [!video link] instead
• Fix a couple of additional markdown display issues
  (Following changes for Uno core repo: docs: Fix multiple docfx, css, js, mermaid layout related issues uno#16972)

---

This is an automatic backport of pull request #1148 done by [Mergify](https://mergify.com). + manual backport of #1097 and #1104.

[mergify]

Cherry-pick of 9f811e5 has failed:

On branch mergify/bp/release/stable/6.0/pr-1148
Your branch is up to date with 'origin/release/stable/6.0'.

You are currently cherry-picking commit 9f811e5.
  (fix conflicts and run "git cherry-pick --continue")
  (use "git cherry-pick --skip" to skip this patch)
  (use "git cherry-pick --abort" to cancel the cherry-pick operation)

Changes to be committed:
	modified:   doc/controls/DrawerFlyoutPresenter.md
	modified:   doc/controls/ExtendedSplashScreen.md
	modified:   doc/controls/LoadingView.md
	modified:   doc/controls/NavigationBar.md
	modified:   doc/controls/ResponsiveView.md
	modified:   doc/controls/SafeArea.md
	modified:   doc/controls/ShadowContainer.md
	modified:   doc/getting-started.md
	modified:   doc/helpers/StatusBar-extensions.md
	modified:   doc/helpers/resource-extensions.md
	modified:   doc/lightweight-styling.md
	modified:   doc/toc.yml

Unmerged paths:
  (use "git add/rm <file>..." as appropriate to mark resolution)
	deleted by us:   build/workflow/stage-determine-changes.yml

To fix up this pull request, you can check it out locally. See documentation: https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/checking-out-pull-requests-locally