Add several new Sniffs from the Universal standard

[jaymcp]

Description

Adds Sniffs to:

• disallow dirname( __FILE__ ) calls (use __DIR__ instead).
• disallow dirname( dirname( ... ) ) calls (use dirname( ..., n ) instead, where n is the number of directories to traverse.
• disallow mixing integer and string keys for array items.
• disallow mixing keyed and unkeyed array items.
• enforce alphabetical sorting of extends and implements names.

Also updates a couple of Sniff exclusions to exclude full Sniffs, rather than specific error codes.

Types of changes (if applicable):

• Bug fix (non-breaking change which fixes an issue).
• New feature (non-breaking change which adds functionality).
• Breaking change (fix or feature that would cause existing functionality to not work as expected).

Checklist (if applicable):

• All checks pass when running `composer run all-checks.