Separate Functional and Unit Test Modes

[agubler]

Producing the unit and functional test bundles in the same mode (test) is problematic, as there is no way to ensure that only the unit.js and functional.js files need would be created. The build would on non-legacy builds (depending on configuration and project code) create extra bundles meaning that neither the unit.js or functional.js bundle would be correct and would cause the test commands to fail.

These changes introduce two new modes unit and functional to the build command that provide explicit instructions on which bundle is needed and enables the build to ensure there is always only a single output bundle produced.

The existing test mode has been deprecated and will only produce the unit bundle now and produce a warning to consumers about moving to the unit or functional modes.

Limited support for the test mode will be removed in the major release after 4.0.0. The test mode will continue to product the unit bundle as this is the most common usage.