[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/optional_scalars/OptionalByte.kt

@@ -3,12 +3,11 @@
 package optional_scalars
 
 @Suppress("unused")
+@kotlin.ExperimentalUnsignedTypes
 class OptionalByte private constructor() {
     companion object {
         const val None: Byte = 0
         const val One: Byte = 1
         const val Two: Byte = 2
-        val names : Array<String> = arrayOf("None", "One", "Two")
-        fun name(e: Int) : String = names[e]
     }
 }

tests/optional_scalars/ScalarStuff.kt

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