Refactor test.cpp (#7487)

* Add timing command to cmakelist

* Start to split test.cpp. Move flexbuffers tests

* Move monster related tests to own file

* Move parser related tests to own file

* Move json related tests to own file

* Move proto related tests to own file

* moved more functions to parser test

* moved more functions to parser test2

* move monster extra tests to monster test

* move evolution tests to own file

* move reflection tests to own file

* move util tests to own file

* rehomed various tests

* move optional scalars test to own file:

* rehome more tests

* move fuzz tests. Got rid of global test_data_path

* fixes for CI failures

* add bazel files

tests/optional_scalars_test.h

@@ -0,0 +1,13 @@
+#ifndef TESTS_OPTIONAL_SCALARS_TEST_H
+#define TESTS_OPTIONAL_SCALARS_TEST_H
+
+
+namespace flatbuffers {
+namespace tests {
+
+void OptionalScalarsTest();
+
+}  // namespace tests
+}  // namespace flatbuffers
+
+#endif