Use legacy rules for ESPHome entity_id construction if friendly_name is unset

[bdraco]

Proposed change

Since we reverted the change to prepend the device name in #97488 , we should also revert the entity_id construction change for legacy naming

fixes #97558

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 #
• This PR is related to issue:
• Link to documentation pull request: Document friendly and legacy rules in ESPHome home-assistant.io#28396

Checklist

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[home-assistant]

Hey there @OttoWinter, @jesserockz, mind taking a look at this pull request as it has been labeled with an integration (esphome) you are listed as a code owner for? Thanks!

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[frenck]

Thanks, @bdraco 👍

../Frenck