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/builder/value.rs

@@ -129,9 +129,10 @@ impl Value {
         !self.is_inline()
     }
     pub fn is_key(&self) -> bool {
-        match self {
-            Value::Key(_) => true,
-            _ => false,
+        if let Value::Key(_) = self {
+            true
+        } else {
+            false
         }
     }
     pub fn is_typed_vector_or_map(&self) -> bool {