Ensure that we have seenAffectedFiles map when files are added to pending emit because they were present in the old state (#37302)

* Make the systems for baselining default to pretty

* Ensure that we have seenAffectedFiles map when files are added to pending emit because they were present in the old state
This happens in build scenarios since semantic diagnostics are queried before emit and hence files are added to seenAffectedFiles pending emit
Fixes #37269

src/harness/virtualFileSystemWithWatch.ts

@@ -445,6 +445,11 @@ interface Array<T> { length: number; [n: number]: T; }`
             this.reloadFS(fileOrFolderorSymLinkList);
         }
 
+        // Output is pretty
+        writeOutputIsTTY() {
+            return true;
+        }
+
         getNewLine() {
             return this.newLine;
         }