Add view in More Info to show entities within a group

[dolfelt]

Proposed change

This proposed change adds an icon to the More Info dialog (see screenshots) that allows you to show and control all the entities within that group. It shows them in a grid pattern using the existing more info controls.

This seems very useful for entities that are controlled simultaneously most of the time, but not all the time. It also helps to simplify dashboards, especially for tablets. Instead of having to have every shade have a tile, one group can be created, and every entity within it can be 2 taps away from being controlled.

Looking forward to feedback and suggestions on everything from code to UI style.

Type of change

• [ ] Dependency upgrade
• [ ] Bugfix (non-breaking change which fixes an issue)
• [x] New feature (thank you!)
• [ ] Breaking change (fix/feature causing existing functionality to break)
• [ ] Code quality improvements to existing code or addition of tests

Example configuration

No additional configuration necessary. Though I was considering adding something to allow this option to be turned on/off for each group. But given how minimal the icon is, it seemed unnecessary.

Additional information

• This PR fixes or closes issue: fixes #15192
• This PR is related to issue or discussion: #15192
• Link to documentation pull request: N/A

Checklist

• [x] The code change is tested and works locally.
• [x] There is no commented out code in this PR.
• [ ] Tests have been added to verify that the new code works.

  There doesn't seem to be any tests in this area of the code. What should I do?

If user exposed functionality or configuration variables are added/changed:

• [ ] Documentation added/updated for www.home-assistant.io

  Documentation seems unnecessary. Let me know if I'm wrong.