Migrate deprecations in core, compiler, idea, tests

Replacing deprecated Char.toInt() with Char.code and
Number.toChar() with Number.toInt().toChar(), where Number is not Int.

KT-23451

compiler/backend/src/org/jetbrains/kotlin/codegen/range/PrimitiveNumberRangeIntrinsicRangeValue.kt

@@ -131,7 +131,7 @@ abstract class PrimitiveNumberRangeIntrinsicRangeValue(
                 if (isProhibitedCharConstEndValue(step, endCharValue))
                     null
                 else
-                    createConstBoundedIntForLoopGenerator(codegen, forExpression, startValue, endCharValue.toInt(), step, isStartInclusive)
+                    createConstBoundedIntForLoopGenerator(codegen, forExpression, startValue, endCharValue.code, step, isStartInclusive)
             }
 
             is LongValue -> {

compiler/backend/src/org/jetbrains/kotlin/codegen/state/SignatureDumpingBuilderFactory.kt

@@ -140,8 +140,8 @@ private fun jsonEscape(value: String): String = buildString {
             '\r' -> append("\\r")
             '\"' -> append("\\\"")
             '\\' -> append("\\\\")
-            else -> if (ch.toInt() < 32) {
-                append("\\u" + Integer.toHexString(ch.toInt()).padStart(4, '0'))
+            else -> if (ch.code < 32) {
+                append("\\u" + Integer.toHexString(ch.code).padStart(4, '0'))
             }
             else {
                 append(ch)