Add and apply Style/InvertibleUnlessCondition rule

This rule was added in rubocop 1.44.0. It's useful to avoid accidental
`unless !condition` clauses.

Note we aren't replacing `unless zero?` with `if nonzero?` because we
never use `nonzero?`; using it sounds like `if !zero?`.

Replacing `unless any?` with `if none?` is only consistent if we also replace
`unless present?` with `if blank?`, so we're also adding this case. For
consistency, we're also replacing `unless blank?` with `if present?`.

We're also simplifying code dealing with `> 0` conditions in order to
make the code (hopefully) easier to understand.

Also for consistency, we're enabling the `Style/InverseMethods` rule,
which follows a similar idea.

.rubocop.yml

@@ -637,6 +637,16 @@ Style/IdenticalConditionalBranches:
 Style/IfWithBooleanLiteralBranches:
   Enabled: true
 
+Style/InverseMethods:
+  Enabled: true
+
+Style/InvertibleUnlessCondition:
+  Enabled: true
+  InverseMethods:
+    :blank?: :present?
+    :present?: :blank?
+    :zero?: ~
+
 Style/LineEndConcatenation:
   Enabled: true