fix(playground): set auto run on clear

[OnkarRuikar]

• Fix Clear in shared Playground doesn't clear properly #663

Issues

The PR addresses the following issues in the playground:

1. In a freshly loaded playground, after clearing, it doesn't auto-run the code.

2. After clearing, the report message(Seeing something inappropriate?) toast doesn't go away.
3. The report message doesn't go away after closing the report dialog.
4. There is no close/dismiss button on the report toast/banner.

Solution

• For the first issue, when the clear button is clicked, set the _autoRun and runOnChange variables.
  - For the second issue, use ${this._gistId && this._showReportToast condition and hide the toast message on clear button click.
  - For the third and fourth issues, define a new toast element named MDNToast to show dismissable messages. Toasts are lightweight, dismissible notifications.

Related issues and pull requests

Fix #663

[caugner]

@OnkarRuikar Thank you for taking the time to work on these changes.

For all the issues that you're addressing in this PR, and that don't have an issue yet, can you please create one? I think they should first go through triage, before we can accept fixes.

That said, if you could extract the fixes for #663 into a separate PR, that would be great to land that fix earlier.

[caugner]

Skimmed over the changes, and left some comments here and there.

[caugner]

This should probably happen as part of controller.clear().

Suggested change

controller.runOnChange = true;

[OnkarRuikar]

done

[OnkarRuikar]

done

[OnkarRuikar]

For all the issues that you're addressing in this PR, and that don't have an issue yet, can you please create one? I think they should first go through triage, before we can accept fixes.

Created separate issues:

• Clear in shared Playground doesn't remove report inappropriate content message #709
• Playground: Seeing something inappropriate? hint doesn't have dismiss/close button #710
• Playground: Seeing something inappropriate? hint doesn't go away after reporting #711

That said, if you could extract the fixes for #663 into a separate PR, that would be great to land that fix earlier.

Let's fix #663 here itself and rest of the stuff in separate PRs after triages there.