New interface (issue project-chip#10249) and new implementation (issue project-chip#10250).

Implementation is all in-memory and uses only static storage and stack
(no heap).

Some details missing (e.g. CAT support) but most is here, though not yet
hooked up to other code.

Comes with unit tests.

Was added at last minute, missed this spot.

- rewrite portions of the check loop to use boolean instead of goto
- refactor privilege checking to make it clearer
- ensure storage classes are POD types (with static_assert)
- remove memsets on storage classes (for now, can re-add later)
- clarify some comments
- remove debug log statement

Also fix some compiler warnings/errors on other builds

Refactor the index conversion (to/from fabric filtered) to be clearer.

- change Target::Flags from int to unsigned
- use unsigned in static_asserts for flags
- tweak auto variables

- Add API documentation (mainly to clarify in/out parameters).
- Add implementation comments (where warranted).
- Add more unit tests (mainly for removing subjects/targets).
- A few fixes to get aforementioned tests passing.
- A bit of refactoring/renaming to clarify the code.