Introduce Char.MIN_VALUE and MAX_VALUE constants (KT-21763)

Add Char.MIN_VALUE and Char.MAX_VALUE implementations in primitive companion objects.
Update builtins test data and public API.

Co-authored-by: Oskar Drozda <themppsplx@gmail.com>

core/builtins/native/kotlin/Char.kt

@@ -62,6 +62,18 @@ public class Char private constructor() : Comparable<Char> {
     public fun toDouble(): Double
 
     companion object {
+        /**
+         * The minimum value of a character code unit.
+         */
+        @SinceKotlin("1.3")
+        public const val MIN_VALUE: Char = '\u0000'
+
+        /**
+         * The maximum value of a character code unit.
+         */
+        @SinceKotlin("1.3")
+        public const val MAX_VALUE: Char = '\uFFFF'
+
         /**
          * The minimum value of a Unicode high-surrogate code unit.
          */