When running `yarn start` and `yarn serve-and-sync`, we are usually
more interested in faster re-build times than optimized builds. This was
also the behavior, before upgrading to @angular/cli@6 (fc5af69fb).
This commit introduces a new configuration (`fast`), which is used by
`yarn start` and `yarn serve-and-sync` to restore the faster,
unoptimized builds.
Other commands, such as `ng serve` and `ng e2e`, remain unchanged (using
slower, optimized builds).
PR Close#23569
George Kalpakas
Filipe Silva
Igor Minar