Use platform-agnostic file separators (#890)

* Use platform-agnostic path separators

* Fix file settings by fixing absolute file path

* Fix missing home link in AppHeader

* Found so many more instances of raw "/" characters

* Tiny Settings style fix

* Clean up onboarding behavior for XState and multi-file

src/hooks/useAbsoluteFilePath.ts

@@ -7,6 +7,6 @@ export function useAbsoluteFilePath() {
   return (
     paths.FILE +
     '/' +
-    encodeURIComponent(routeData?.project?.path || BROWSER_FILE_NAME)
+    encodeURIComponent(routeData?.file?.path || BROWSER_FILE_NAME)
   )
 }