Minor improvements to path include/exclude logic

[ecraig12345]

Update getScopedPackages to skip the step of checking for package inclusion if there are only exclusion (negated) scope patterns specified. This should provide a minor efficiency improvement in large repos.

Also update isPathIncluded's include parameter (and the group include options that use it) to allow passing true instead of include pattern(s), to include all packages except those specified by exclude and skip some pattern checks.

Other changes:

• Simplify isPathIncluded logic
• Add more tests for isPathIncluded
• Update docs for group exclude to clarify that exclusions must be specified as negated patterns for now (this is an incorrect design which should be fixed in a major version, tracked by Fix behavior of group "exclude" options #916)