[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/expressionAsFunctionBody.kt

@@ -4,4 +4,4 @@ fun box() =
 fun foo() =
         23
 
-// LINES: 2 2 2 5 5 5
+// LINES: 1 2 2 4 5 5