JS: use '/' as separator on all platforms to prevent sourcemap parse errors

js/js.translator/src/org/jetbrains/kotlin/js/sourceMap/SourceMap3Builder.java

@@ -127,6 +127,9 @@ public class SourceMap3Builder implements SourceMapBuilder {
 
     @Override
     public void addMapping(String source, int sourceLine, int sourceColumn) {
+        if (File.separatorChar != '/') {
+            source = source.replace(File.separatorChar, '/');
+        }
         boolean newGroupStarted = previousGeneratedColumn == -1;
         if (newGroupStarted) {
             previousGeneratedColumn = 0;