Support ^ reverse / parent navigation in find and criteria

[jtnelson]

Tracks the Runway side of reverse / parent navigation. Parent feature:
cinchapi/concourse#781.

Summary

Let Runway find and criteria use reverse-navigation keys (^, ^key) so
application code can query records by their parents, for example
find(File.class, where("^.exchange.user.userId").EQUALS.value(me)).

Scope

• Pass ^-keyed criteria through to the server unchanged; the server resolves
  them.
• Treat a ^-keyed condition as database-resolvable.
• Client-side parity: teach Record.matches and navigate to evaluate reverse
  hops so in-memory matching agrees with server find.
• Gate behind a supportsReverseNavigation server-version check (mirroring
  supportsTransitiveNavigation), falling back to the existing
  find-then-collect idiom on older servers.
• Optional stretch: an @Inverse(from, via) field annotation plus a
  linkedFrom(...) accessor that resolve a declared back-reference (compiling
  to the same primitive) for an ORM-ergonomic parent read site.

Acceptance Criteria

• A find with a ^ or ^key criterion returns the correct records via
  the server.
• matches() agrees with find() for reverse criteria.
• The version gate degrades gracefully on servers without
  reverse-navigation support.
• Tests cover bare ^, ^key, and a multi-hop reverse criterion (the
  my-files query) against Mockcourse and Runway.