Add an index for devices and config entries to the entity registry

[bdraco]

Proposed change

As more entities have been added, the run time cost of looking up entities by device and config entries has increased. For reference, the entity registry storage is now 4-5MB on most of my production systems. The number of entities in the registry continues to grow as more integrations are updated so the problem will continue to get worse over time.

More integrations have migrations of unique ids which tend to stay in the code base for a very long time. They are frequent callers of er.async_entries_for_device and er.async_entries_for_config_entry. Both of these functions have to do a linear search over the entire registry to find matching entries since there is no index for device_id or config_entry id

Side node: Ideally we would change these functions to return a set in another set so removing the the index is cheap, but a lot of the tests are expecting explicit order because its been a list even though its not needed

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)
• Deprecation (breaking change to happen in the future)
• 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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[bdraco]

thanks