* doc/guix.texi (Invoking guix environment): Add --no-cwd.
* guix/scripts/environment.scm (show-help, %options): Add --no-cwd.
(launch-environment/container): Add 'map-cwd?' param; only add mapping
for cwd if #t.  Only change to cwd within container if #t, otherwise
home.
(guix-environment): Error if --no-cwd without --container.  Provide
'(not no-cwd?)' to launch-environment/container as 'map-cwd?'.
* tests/guix-environment.sh: Add test for no-cwd.

Co-authored-by: Mike Gerwitz <mtg@gnu.org>