Before this, we had several places where an isReleaseMode was defined, all with the same definition. This just makes it more broadly visible to allow our users to use it, as well as creating debug and profile versions, and adding a device lab test for it.
Since this is a const value, this makes it possible for a developer to easily mark blocks that can be removed at AOT compile time.
Disallow calling stop() or cancel() multiple times. This means that
when you use startProgress you have to more carefully think about what
exactly is going on.
Properly cancel startProgress in non-ANSI situations, so that
back-to-back startProgress calls all render to the console.
