We were previously only looking at the `cellar` value when pouring
bottles and ignoring the `prefix` and (implicit) `repository`.
Actually look at these values and set the defaults for each platform.
Also, when we're relocating to create or pour bottles when `prefix`
and `repository` are equal then skip relocating the `repository` and
always use references to the `prefix` instead.
Fixes#9453
Refactor the CLI::Args module so it doesn't have different paths to
check arguments depending on whether the arguments have been parsed or
not. Instead, set the values we need from the global ARGV at
first, global initialisation time where they will be thrown away when
the actual arguments are parsed.
To do this some other general refactoring was needed:
- more methods made private when possible
- e.g. `HEAD?` used consistently instead of `head` before arguments
are parsed.
- formula options are only parsed after named arguments are extracted
