[overnet] Get things ready for use.

This is relanding a previous change, with host side fuzzing fixed.

Allow FIDL messages (including channel handles) to be propagated between
overnet instances.

Add an example suite in Rust.

Refactor the overnet app to better separate concerns.

Propagate service & routing information between nodes.

Clean up tracing API's.

Initial crypto support.

Enable one fuzzer.

Reorganize files in lib/overnet.

Rewrite/fix packet loss handling.

Test: all unit tests pass, compiled locally with fx set x64 to verify host side fuzzers no longer cause problems.

Change-Id: Id30f4dbb1567e4e8d0d4efb7955b01a76f158ddb
167 files changed