* [Kotlin] Control the generation of reflection with --reflect-names.
Tested:
```
$ cmake -G "Unix Makefiles" && make && ./tests/flatc/main.py
...
KotlinTests.EnumValAttributes
[PASSED]
KotlinTests.EnumValAttributes_ReflectNames
[PASSED]
KotlinTests: 2 of 2 passsed
...
35 of 35 tests passed
```
* [Kotlin] Fix SampleBinary by converting Byte to UByte for ubyte fields.
* [Kotlin] Annotate all generated classes with kotlin.ExperimentalUnsignedTypes.
* Add test for optional enums in Kotlin
* Rename optional_scalars2.fbs into optional_scalars.fbs
Also updated all references in the project to point to
"optional_scalars.fbs" instead of "optional_scalars2.fbs".
Anton Bobukh