[Kotlin] Control the generation of reflection with --reflect-names (#7775)

* [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.

tests/MyGame/Example/StructOfStructsOfStructs.kt

@@ -19,6 +19,7 @@ import java.nio.ByteOrder
 import kotlin.math.sign
 
 @Suppress("unused")
+@kotlin.ExperimentalUnsignedTypes
 class StructOfStructsOfStructs : Struct() {
 
     fun __init(_i: Int, _bb: ByteBuffer)  {