Moves files generated in windows/flutter/ as part of the build to an ephemeral/ subdirectory, matching the approach used on macOS (and in the future, Windows).
Adds that directory to the generated properties file to minimize hard-coding of paths in the project.
When building in profile or release mode on desktop, add a prominent
warning that it's actually a debug build. This is to help address issues
with people being unaware of the current state of builds due to
following third-party guides rather than official documentation.
macOS is not included since PRs are in flight for macOS release support.
