Split off ZHA diagnostics files without an original signature

[puddly]

Effectively, device dumps sourced from diagnostics prior to ZHA having original_signature are separated out into legacy_devices/. Everything in devices/ should be accurate (for the most part, not accounting for ZCL attribute mutation).

The diff will display strangely but the individual commits should make the changes clear.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 97.27%. Comparing base (a0e3195) to head (2ffa1ca).

Additional details and impacted files

@@            Coverage Diff             @@
##              dev     #803      +/-   ##
==========================================
- Coverage   97.29%   97.27%   -0.02%     
==========================================
  Files          55       55              
  Lines       10933    10935       +2     
==========================================
  Hits        10637    10637              
- Misses        296      298       +2     

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[TheJulianJES]

I thought this was just #788 at first but that's something different. Then thought this should be a separate PR. But looking at the code, we never read self._state – it's only ever set. I think we can just remove self._state entirely then? is_on does access the attribute value directly, like all other entities (but that's guarded by is_supported() then).