Stop relying on `MM::Device::GetName()` for `CMMCore::getDeviceName()`

[marktsuchida]

MMCore should just store the device name used at creation time and return it.

This would mean that device adapters' GetName() implementations would only be used in the case of of peripheral device discovery (which should stop using device objects entirely, but that's a separate issue).

See #649 for background.

Cf. pymmcore-plus/pymmcore-plus#592