support "extends" from embassy data. (#351)

* Update generate.zig

Attempted to support "extends" syntax in register json files

* updated generated code.

* clean up names

* fixed a few stragglers

* Apply suggestions from code review

its easy to miss a few.

Co-authored-by: Matt Knight <mattnite@proton.me>

* More Name Cleanup.

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Co-authored-by: Matt Knight <mattnite@proton.me>

Author: taylorh140