JavaScript: Fix existing tests and test runner

Fixes two things:
- The basic test should no longer extract `tst.js` (as `tst.ts` is
  present)
- The `AutoBuild` mock did not populate `extractedFiles` correctly,
  which broke the logic that looks for TypeScript files with the same
  basename.

javascript/extractor/test/com/semmle/js/extractor/test/AutoBuildTests.java

@@ -135,6 +135,7 @@ public class AutoBuildTests {
             FileExtractors extractors) {
           for (Path f : files) {
             actual.add(f.toString());
+            extractedFiles.add(f);
           }
         }
 
@@ -175,7 +176,7 @@ public class AutoBuildTests {
 
   @Test
   public void basicTest() throws IOException {
-    addFile(true, LGTM_SRC, "tst.js");
+    addFile(false, LGTM_SRC, "tst.js");
     addFile(true, LGTM_SRC, "tst.ts");
     addFile(true, LGTM_SRC, "tst.html");
     addFile(true, LGTM_SRC, "tst.xsjs");