WASM: Implement wasm-native strings part 1

There are several changes here but they all required for at least one test to pass.
- Implemented String class and several utility functions using built-in CharArray
- Added new constant memory segment to hold string literals and required funcs to work with them
- Added very crude mostly incorrect rudimentary ability to pass strings back to javascript

libraries/stdlib/wasm/builtins/kotlin/Char.kt

@@ -154,7 +154,3 @@ public class Char private constructor(public val value: Char) : Comparable<Char>
         public const val SIZE_BITS: Int = 16
     }
 }
-
-@WasmImport("runtime", "Char_toString")
-private fun charToString(c: Char): String = implementedAsIntrinsic
-