Rust Object API (#6070)

* inital commit of rust object api

* Required fields support.

* clang fallthrough

* Fix unused variables

* just don't fall through

* remove comment

* s/panic/unreachable

* Tests for object API

* Added defaults

* deleted unintentionally added files and updated .bat file

* fix bat file

* clang format

* Cargo clippy checks

* remove commented out code

* clippy allows

* Remove matches! macro since we're not yet at Rust v1.42

* install clippy in RustTest.sh

* move line

Co-authored-by: Casper Neo <cneo@google.com>

rust/flexbuffers/src/lib.rs

@@ -28,6 +28,10 @@
 //             Serializable structs are Pushable
 //             Serde with maps - field names and type names.
 
+// Until flat/flexbuffers is on Rust v1.42, we cannot use the previously unstable matches! macro.
+#![allow(clippy::unknown_clippy_lints)]
+#![allow(clippy::match_like_matches_macro)]
+
 #[macro_use]
 extern crate bitflags;
 extern crate byteorder;