controllers: refactor rate limits.

Refactor controllers so that endpoint rate limits are declared locally,
with the endpoint, instead of globally, in a single method in ApplicationController.

This way an endpoint's rate limit is declared in the same file as the
endpoint itself.

This is so we can add fine-grained rate limits for certain GET requests.
Before rate limits were only for non-GET requests.

app/logical/rate_limiter.rb

@@ -21,34 +21,19 @@ class RateLimiter
     @burst = burst
   end
 
-  # Create a RateLimiter object for the current controller, action, user, and
-  # IP. A RateLimiter usually has two RateLimits, one for the user and one for
-  # their IP. The action is limited if either the user or their IP are limited.
+  # Create a RateLimiter object for the given action. A RateLimiter usually has
+  # two RateLimits, one for the user and one for their IP. The action is
+  # limited if either the user or their IP are limited.
   #
-  # @param controller_name [String] the current controller
-  # @param action_name [String] the current controller action
-  # @param user [User] the current user
-  # @param ip_addr [String] the user's IP address
-  # @return [RateLimit] the rate limit for the action
-  def self.for_action(controller_name, action_name, user, ip_addr)
-    action = "#{controller_name}:#{action_name}"
+  # @param action [String] An identifier for the action being rate limited.
+  # @param rate [Float] The rate limit, in actions per second.
+  # @param burst [Float] The burst limit (the maximum number of actions you can
+  #   perform in one burst before being rate limited).
+  # @param user [User] The current user.
+  # @param ip_addr [String] The user's IP address.
+  # @return [RateLimit] The rate limit for the action.
+  def self.build(action:, rate:, burst:, user:, ip_addr:)
     keys = [(user.cache_key unless user.is_anonymous?), "ip/#{ip_addr.to_s}"].compact
-
-    case action
-    when "users:create"
-      rate, burst = 1.0 / 5.minutes, 10
-    when "emails:update", "sessions:create", "moderation_reports:create"
-      rate, burst = 1.0 / 1.minute, 10
-    when "dmails:create", "comments:create", "forum_posts:create", "forum_topics:create"
-      rate, burst = 1.0 / 1.minute, 50
-    when "comment_votes:create", "comment_votes:destroy", "post_votes:create",
-         "post_votes:destroy", "favorites:create", "favorites:destroy", "post_disapprovals:create"
-      rate, burst = 1.0 / 1.second, 200
-    else
-      rate = user.api_regen_multiplier
-      burst = 200
-    end
-
     RateLimiter.new(action, keys, rate: rate, burst: burst)
   end