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

js/js.frontend/src/org/jetbrains/kotlin/js/resolve/diagnostics/JsCallChecker.kt

@@ -167,7 +167,7 @@ private fun String.offsetOf(position: CodePosition): Int {
         i++
         offsetInLine++
 
-        if (isEndOfLine(c.toInt())) {
+        if (isEndOfLine(c.code)) {
             offsetInLine = 0
             lineCount++
             assert(lineCount <= position.line)

js/js.frontend/src/org/jetbrains/kotlin/js/resolve/diagnostics/jsRenderers.kt

@@ -80,7 +80,7 @@ fun String.underlineAsText(from: Int, to: Int): String {
         marks.append(mark)
         lineWasMarked = lineWasMarked || mark != ' '
 
-        if (isEndOfLine(c.toInt())) {
+        if (isEndOfLine(c.code)) {
             if (lineWasMarked) {
                 lines.appendLine(marks.toString().trimEnd())
                 lineWasMarked = false
@@ -121,7 +121,7 @@ fun String.underlineAsHtml(from: Int, to: Int): String {
 
         lines.append(mark)
 
-        if (isEndOfLine(c.toInt()) && openMarker) {
+        if (isEndOfLine(c.code) && openMarker) {
             lines.append(underlineEnd + c + underlineStart)
         } else {
             lines.append(c)