Use global --resolver option parsing for stack init

[harendra-kumar]

stack init implements its own --resolver command line option which seem to be doing exactly the same thing as the global --resolver option implementation.

We can avoid this duplication by deleting the parsing code in initOptsParser and passing the resolver value from globalOpts in initCmd.

See also #1531.

[mgsloan]

Makes sense!

[borsboom]

stack init's --resolver is slightly different because it selects the behaviour (note the usage has ([--solver] | [--resolver RESOLVER] | [--prefer-lts] | [--prefer-nightly])), so fixing this may be a bit more involved as you'll have to ensure none of the other local options (--solver, --prefer-lts, --prefer-nightly) were given if the global --resolver is set.

[harendra-kumar]

Ah, I missed this point earlier.

The init options have changed a bit with PR #1583 though. --resolver can now be specified with --solver. So we have to take care of --prefer-lts and --prefer-nightly only, but that does not change the order of effort.

Usage: stack init ([--resolver RESOLVER] | [--prefer-lts] | [--prefer-nightly])
                  [--solver] [--force] [--ignore-subdirs] [--help]
  Initialize a stack project based on one or more cabal packages