Add minor improvement to kotlin String literals in generated sources

Interop/StubGenerator/src/main/kotlin/org/jetbrains/kotlin/native/interop/gen/CodeUtils.kt

@@ -48,21 +48,27 @@ fun String.asSimpleName(): String = if (this in kotlinKeywords) {
  * Returns the expression to be parsed by Kotlin as string literal with given contents,
  * i.e. transforms `foo$bar` to `"foo\$bar"`.
  */
-fun String.quoteAsKotlinLiteral(): KotlinExpression {
+fun String.quoteAsKotlinLiteral(): KotlinExpression = buildString {
-    val sb = StringBuilder()
+    append('"')
-    sb.append('"')
 
-    this.forEach { c ->
+    this@quoteAsKotlinLiteral.forEach { c ->
-        val escaped = when (c) {
+        when (c) {
-            in 'a' .. 'z', in 'A' .. 'Z', in '0' .. '9', '_', '@', ':', '{', '}', '=', '[', ']', '^', '#', '*' -> c.toString()
+            in charactersAllowedInKotlinStringLiterals -> append(c)
-            '$' -> "\\$"
+            '$' -> append("\\$")
-            else -> "\\u" + "%04X".format(c.toInt()) // TODO: improve result readability by preserving more characters.
+            else -> append("\\u" + "%04X".format(c.toInt()))
         }
-        sb.append(escaped)
     }
 
-    sb.append('"')
+    append('"')
-    return sb.toString()
+}
+
+// TODO: improve literal readability by preserving more characters.
+
+private val charactersAllowedInKotlinStringLiterals: Set<Char> = mutableSetOf<Char>().apply {
+    addAll('a' .. 'z')
+    addAll('A' .. 'Z')
+    addAll('0' .. '9')
+    addAll(listOf('_', '@', ':', ';', '.', ',', '{', '}', '=', '[', ']', '^', '#', '*', ' '))
 }
 
 fun block(header: String, lines: Iterable<String>) = block(header, lines.asSequence())