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.

app/controllers/proposals_controller.rb

@@ -155,8 +155,8 @@ class ProposalsController < ApplicationController
     end
 
     def load_featured
-      return unless !@advanced_search_terms && @search_terms.blank? &&
-                    params[:retired].blank? && @current_order != "recommendations"
+      return if @advanced_search_terms || @search_terms.present? ||
+                params[:retired].present? || @current_order == "recommendations"
 
       if Setting["feature.featured_proposals"]
         @featured_proposals = Proposal.not_archived