Add support for using array of scalar as key field in Cpp (#7623)

* add support for using array of scalar as key field

* update cmakelist and test.cpp to include the tests

* update bazel rule

* address comments

* clang format

* delete comment

* delete comment

* address the rest of the commnets

* address comments

* update naming in test file

* format build file

* buildifier

* make keycomparelessthan call keycomparewithvalue

* update to use flatbuffer array instead of raw pointer

* clang

* format

* revert format

* revert format

* update

* run generate_code.py

* run code generator

* revert changes by generate_code.py

* fist run make flatc and then run generate_code.py

Co-authored-by: Wen Sun <sunwen@google.com>

tests/key_field_test.h

@@ -0,0 +1,12 @@
+#ifndef TESTS_KEY_FIELD_TEST_H
+#define TESTS_KEY_FIELD_TEST_H
+
+namespace flatbuffers {
+namespace tests {
+
+void FixedSizedScalarKeyInStructTest();
+
+}  // namespace tests
+}  // namespace flatbuffers
+
+#endif