This style change enforces `return if ...` instead of
`return nil if ...` to save maintainers a few minor review points

Enables frozen for the following:

* lib/*.rb
* lib/banzai/**/*.rb
* lib/bitbucket/**/*.rb
* lib/constraints/**/*.rb
* lib/container_registry/**/*.rb
* lib/declarative_policy/**/*.rb

Partially addresses #47424.

Adds a rubocop rule (with autocorrect) to ensure line break after guard clauses.

Both `Or` and `And` would evaluate whether each rule passed, then calculate a
value based on the results of all of those. We can actually return early in many
cases, without running the rule at all.