bug(datepicker): Improper focus & allowing to focus on background elements of calendar dialog

[zarend]

Reproduction

Steps to reproduce:

1. Open the Datepicker Examples
2. Go to the "Basic datepicker" demo
3. Linear navigate till the end of the dialog
4. Linear navigate forward

Expected Behavior

It should not allow to navigate to the background elements, when calendar dialog is open

Actual Behavior

It is allowing to focus on the background elements of the open calendar dialog.

1. It is showing the focus on last element edit box, when open calendar dialog on first element edit box & linear navigate back.
2. It is focusing on the darkmode & strong focus toggles, when linear navigate forward after reaching end of calendar dialog using ChromeVox

Environment

OS| Browser | Screen reader
ChromeOS | Google Chrome 91.0.4472.167 | ChromeVox
macOS Catalina | Google Chrome 92.0.4515.131 | VoiceOver

Additional Notes

This is copied from an internal bug report found during a11y testing.

[zarend]

TL;DR: focus trapping seems to not be set up in the same configuration for datepicker as it is for MatDialog which already solves this. They should be set to use the same configuration.

[zarend]

This was fixed by #24300

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