Run CI tests on Windows, Macos and Linux

[AngheloAlf]

Follow up PR for #443

• Now we run our CI tests on Windows and Macos too, so we can see everything works mostly the same in every platform.
  • For this test we were building a fake rom to feed to splat using KMC. Since we don't build KMC for Windows we decided to commit the fake rom to the repo. We still build this rom from scratch on Linux CI to ensure the source code and the committed rom do not desync.
  • I also enabled dependency file generation on the basic app yaml since those files are path sensitive too.
• Fix other places that missed the forward slashes on the previous PR.