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.

Slight cleanup of file locations in flutter_tools
to make it easier to see which files are responsible
for data reporting.