[JS BE] Make sourceMap generation more precise

- Don't produce mapping for closing bracket in case of expressionBody
 - Map Kt*Function declaration into corresponding js fun declaration
 - Update test data & add new test

js/js.translator/testData/lineNumbers/whenEntryWithMultipleConditions.kt

@@ -18,4 +18,4 @@ fun box(x: Int) {
     )
 }
 
-// LINES: 19 4 4 3 3 4 6 9 9 6 11 13 13 11 16 16 3 2
+// LINES: 1 19 4 4 3 3 4 6 9 9 6 11 13 13 11 16 16 3 2