JS: rewrite source map generator to use specialized JSON writer

Fixes problems with string escaping. See KT-20005

compiler/testData/cli/js/sourceMapCharEscape.args

@@ -0,0 +1,7 @@
+$TESTDATA_DIR$/sourceMapCharEscape.kt
+-no-stdlib
+-source-map
+-source-map-embed-sources
+always
+-output
+$TEMP_DIR$/out.js

compiler/testData/cli/js/sourceMapCharEscape.kt

@@ -0,0 +1 @@
+fun foo() = "©∑\n"

compiler/testData/cli/js/sourceMapCharEscape.out

@@ -0,0 +1 @@
+OK

compiler/testData/cli/js/sourceMapCharEscape.test

@@ -0,0 +1,2 @@
+// EXISTS: out.js
+// CONTAINS: out.js.map, \"©∑\\n\"\n

compiler/tests/org/jetbrains/kotlin/cli/CliTestGenerated.java

@@ -545,6 +545,12 @@ public class CliTestGenerated extends AbstractCliTest {
             doJsTest(fileName);
         }
 
+        @TestMetadata("sourceMapCharEscape.args")
+        public void testSourceMapCharEscape() throws Exception {
+            String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/cli/js/sourceMapCharEscape.args");
+            doJsTest(fileName);
+        }
+
         @TestMetadata("sourceMapDuplicateRelativePaths.args")
         public void testSourceMapDuplicateRelativePaths() throws Exception {
             String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/cli/js/sourceMapDuplicateRelativePaths.args");