JS backend: don't use octal numbers when render non-latin symbols, because of it prohibited in strict mode

#KT-7921 Fixed

js/js.dart-ast/src/com/google/dart/compiler/backend/js/JsToStringGenerationVisitor.java

@@ -124,40 +124,21 @@ public class JsToStringGenerationVisitor extends JsVisitor {
                 result.append((char) escape);
             }
             else {
-                /*
-                * Emit characters from 0 to 31 that don't have a single character
-                * escape sequence in octal where possible. This saves one or two
-                * characters compared to the hexadecimal format '\xXX'.
-                *
-                * These short octal sequences may only be used at the end of the string
-                * or where the following character is a non-digit. Otherwise, the
-                * following character would be incorrectly interpreted as belonging to
-                * the sequence.
-                */
-                if (c < ' ' && (i == n - 1 || chars.charAt(i + 1) < '0' || chars.charAt(i + 1) > '9')) {
-                    result.append('\\');
-                    if (c > 0x7) {
-                        result.append((char) ('0' + (0x7 & (c >> 3))));
-                    }
-                    result.append((char) ('0' + (0x7 & c)));
+                int hexSize;
+                if (c < 256) {
+                    // 2-digit hex
+                    result.append("\\x");
+                    hexSize = 2;
                 }
                 else {
-                    int hexSize;
-                    if (c < 256) {
-                        // 2-digit hex
-                        result.append("\\x");
-                        hexSize = 2;
-                    }
-                    else {
-                        // Unicode.
-                        result.append("\\u");
-                        hexSize = 4;
-                    }
-                    // append hexadecimal form of ch left-padded with 0
-                    for (int shift = (hexSize - 1) * 4; shift >= 0; shift -= 4) {
-                        int digit = 0xf & (c >> shift);
-                        result.append(HEX_DIGITS[digit]);
-                    }
+                    // Unicode.
+                    result.append("\\u");
+                    hexSize = 4;
+                }
+                // append hexadecimal form of ch left-padded with 0
+                for (int shift = (hexSize - 1) * 4; shift >= 0; shift -= 4) {
+                    int digit = 0xf & (c >> shift);
+                    result.append(HEX_DIGITS[digit]);
                 }
             }
         }

js/js.tests/test/org/jetbrains/kotlin/js/test/semantics/CharTest.java

@@ -50,4 +50,8 @@ public final class CharTest extends SingleFileTranslationTest {
     public void testCharEquals() throws Exception {
         checkFooBoxIsOk();
     }
+
+    public void testCharConstantByUnicodeId() throws Exception {
+        checkFooBoxIsOk();
+    }
 }

js/js.translator/testData/char/cases/charConstantByUnicodeId.kt

@@ -0,0 +1,20 @@
+package foo
+
+fun box(): String {
+    val chars = mapOf('\u0000' to 0x0000,
+                      '\u0001' to 0x0001,
+                      '\u0010' to 0x0010,
+                      '\u001F' to 0x001F,
+                      '\u0064' to 0x0064,
+                      '\u00A0' to 0x00A0,
+                      '\u00FF' to 0x00FF,
+                      '\u0100' to 0x0100,
+                      '\uF01F' to 0xF01F)
+
+    for ((char, code) in chars) {
+        assertEquals(code, char.toInt())
+        assertEquals(char, code.toChar())
+    }
+
+    return "OK"
+}