Update Light extension example to match docs.

This light extension example was more of a POC. Now it
matches the suggestions for minor version requirements
and vendor extensions that are spelled out in publically
available documentation.

This includes things like:
- taking advantage of namespacing rather than renaming things
- adding documentation when extension differs from what a minor
  version extension should be
- importing things specifically rather than dumping namespaces
  into the types.hal file

Test: compilation only -- it doesn't do anything
Change-Id: Ia1bf9baaddcb630cc1b6cd4fe272def0c7c492e9
Fixes: 67787567