Migrate sensor device classes to StrEnum

[frenck]

Breaking change

This PR deprecates the use of the DEVICE_CLASS_* constants and DEVICE_CLASSES constant for sensor entities. Use the SensorDeviceClass enum instead.

Proposed change

Replaces the device class constants of the sensor platform with a StrEnum.

The old CONST is currently still accepted and working (backward compatible). This gives core and custom integration time to adjust.

At this point, I've not set a deprecation period as it is hard to indicate how long this would take.

Type of change

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

Additional information

• This PR fixes or closes issue: fixes #
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Checklist

• The code change is tested and works locally.
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• Tests have been added to verify that the new code works.

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

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[probot-home-assistant]

Hey there @home-assistant/core, mind taking a look at this pull request as it has been labeled with an integration (demo) you are listed as a code owner for? Thanks!
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