Change how files are passed into pw_env_setup. In most cases they're
passed in with --use-pigweed-defaults, but downstream projects now have
the option to not include Pigweed's defaults.
Change-Id: I82383705e156be14276a8498648ca376e3340efb
Bug: 274
Requires: pigweed-internal:7120
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/19380
Commit-Queue: Rob Mohr <mohrr@google.com>
Reviewed-by: Joe Ethier <jethier@google.com>
Reviewed-by: Michael Spang <spang@google.com>
