Add support for online speech recognition (behind a flag)

[freedmand]

Apparently on-device speech recognition is only supported on some Mac devices.

https://support.apple.com/guide/mac-help/if-dictation-on-mac-doesnt-work-as-expected-mchlc480652b/mac:

This issue tracks adding a feature to support speech recognition powered by Apple. Since it would require sending data to Apple's servers, this should not be enabled by default and should require a flag.

Also, the current error: ERROR: Speech recognizer does not support on-device recognition is not too descriptive. It could be revised to include more context or suggest the proposed flag.