Deprecate Char-to-Number conversions in stdlib (JVM and JS)

- Int.toChar was left non-deprecated because the replacement is not intrinsic yet.
- Number.toChar was left non-deprecated because otherwise the deprecation propagates to the override, Int.toChar.

KT-23451

core/builtins/native/kotlin/Char.kt

@@ -47,18 +47,30 @@ public class Char private constructor() : Comparable<Char> {
     public operator fun rangeTo(other: Char): CharRange
 
     /** Returns the value of this character as a `Byte`. */
+    @Deprecated("Conversion of Char to Number is deprecated. Use Char.code property instead.", ReplaceWith("this.code.toByte()"))
+    @DeprecatedSinceKotlin(warningSince = "1.5")
     public fun toByte(): Byte
     /** Returns the value of this character as a `Char`. */
     public fun toChar(): Char
     /** Returns the value of this character as a `Short`. */
+    @Deprecated("Conversion of Char to Number is deprecated. Use Char.code property instead.", ReplaceWith("this.code.toShort()"))
+    @DeprecatedSinceKotlin(warningSince = "1.5")
     public fun toShort(): Short
     /** Returns the value of this character as a `Int`. */
+    @Deprecated("Conversion of Char to Number is deprecated. Use Char.code property instead.", ReplaceWith("this.code"))
+    @DeprecatedSinceKotlin(warningSince = "1.5")
     public fun toInt(): Int
     /** Returns the value of this character as a `Long`. */
+    @Deprecated("Conversion of Char to Number is deprecated. Use Char.code property instead.", ReplaceWith("this.code.toLong()"))
+    @DeprecatedSinceKotlin(warningSince = "1.5")
     public fun toLong(): Long
     /** Returns the value of this character as a `Float`. */
+    @Deprecated("Conversion of Char to Number is deprecated. Use Char.code property instead.", ReplaceWith("this.code.toFloat()"))
+    @DeprecatedSinceKotlin(warningSince = "1.5")
     public fun toFloat(): Float
     /** Returns the value of this character as a `Double`. */
+    @Deprecated("Conversion of Char to Number is deprecated. Use Char.code property instead.", ReplaceWith("this.code.toDouble()"))
+    @DeprecatedSinceKotlin(warningSince = "1.5")
     public fun toDouble(): Double
 
     companion object {

core/builtins/native/kotlin/Number.kt

@@ -43,6 +43,7 @@ public abstract class Number {
     /**
      * Returns the [Char] with the numeric value equal to this number, truncated to 16 bits if appropriate.
      */
+//    @Deprecated("Direct conversion to Char is deprecated. Use toInt().toChar() or Char constructor instead.", ReplaceWith("this.toInt().toChar()"))
     public abstract fun toChar(): Char
 
     /**

core/builtins/native/kotlin/Primitives.kt

@@ -201,6 +201,8 @@ public class Byte private constructor() : Number(), Comparable<Byte> {
      * The least significant 8 bits of the resulting `Char` code are the same as the bits of this `Byte` value,
      * whereas the most significant 8 bits are filled with the sign bit of this value.
      */
+    @Deprecated("Direct conversion to Char is deprecated. Use toInt().toChar() or Char constructor instead.", ReplaceWith("this.toInt().toChar()"))
+    @DeprecatedSinceKotlin(warningSince = "1.5")
     public override fun toChar(): Char
     /**
      * Converts this [Byte] value to [Short].
@@ -442,6 +444,8 @@ public class Short private constructor() : Number(), Comparable<Short> {
      * The resulting `Char` code is equal to this value reinterpreted as an unsigned number,
      * i.e. it has the same binary representation as this `Short`.
      */
+    @Deprecated("Direct conversion to Char is deprecated. Use toInt().toChar() or Char constructor instead.", ReplaceWith("this.toInt().toChar()"))
+    @DeprecatedSinceKotlin(warningSince = "1.5")
     public override fun toChar(): Char
     /** Returns this value. */
     public override fun toShort(): Short
@@ -982,6 +986,8 @@ public class Long private constructor() : Number(), Comparable<Long> {
      *
      * The resulting `Char` code is represented by the least significant 16 bits of this `Long` value.
      */
+    @Deprecated("Direct conversion to Char is deprecated. Use toInt().toChar() or Char constructor instead.", ReplaceWith("this.toInt().toChar()"))
+    @DeprecatedSinceKotlin(warningSince = "1.5")
     public override fun toChar(): Char
     /**
      * Converts this [Long] value to [Short].
@@ -1225,6 +1231,8 @@ public class Float private constructor() : Number(), Comparable<Float> {
      *
      * The resulting `Char` value is equal to `this.toInt().toChar()`.
      */
+    @Deprecated("Direct conversion to Char is deprecated. Use toInt().toChar() or Char constructor instead.", ReplaceWith("this.toInt().toChar()"))
+    @DeprecatedSinceKotlin(warningSince = "1.5")
     public override fun toChar(): Char
     /**
      * Converts this [Float] value to [Short].
@@ -1464,6 +1472,8 @@ public class Double private constructor() : Number(), Comparable<Double> {
      *
      * The resulting `Char` value is equal to `this.toInt().toChar()`.
      */
+    @Deprecated("Direct conversion to Char is deprecated. Use toInt().toChar() or Char constructor instead.", ReplaceWith("this.toInt().toChar()"))
+    @DeprecatedSinceKotlin(warningSince = "1.5")
     public override fun toChar(): Char
     /**
      * Converts this [Double] value to [Short].