Fix broken "Show whitespace changes" button on MR "Changes" tab

This MR fixes the issue where the Show/Hide whitespace changes button was getting stuck in the Show whitespace changes state once it has been toggled.

The problem was that the w=0 parameter in the URL was getting handled as if it was an integer flag. Since url params are always strings the flag will always result in true regardless of the value.

This MR fixes the issue by converting the w flag to an integer when it is read out.

Tests for the component has also been added.

What are the relevant issue numbers?

Closes #52122 (closed)

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Tests added for this feature/bug
• Conforms to the code review guidelines
• Conforms to the merge request performance guidelines

app/finders/issuable_finder.rb

@@ -14,7 +14,7 @@
 #     project_id: integer
 #     milestone_title: string
 #     author_id: integer
-#     assignee_id: integer
+#     assignee_id: integer or 'None' or 'Any'
 #     search: string
 #     label_name: string
 #     sort: string
@@ -34,6 +34,11 @@ class IssuableFinder
 
   requires_cross_project_access unless: -> { project? }
 
+  # This is used as a common filter for None / Any
+  FILTER_NONE = 'none'.freeze
+  FILTER_ANY = 'any'.freeze
+
+  # This is accepted as a deprecated filter and is also used in unassigning users
   NONE = '0'.freeze
 
   attr_accessor :current_user, :params
@@ -236,16 +241,20 @@ def labels
   # rubocop: enable CodeReuse/ActiveRecord
 
   def assignee_id?
-    params[:assignee_id].present? && params[:assignee_id].to_s != NONE
+    params[:assignee_id].present?
   end
 
   def assignee_username?
-    params[:assignee_username].present? && params[:assignee_username].to_s != NONE
+    params[:assignee_username].present?
   end
 
-  def no_assignee?
+  def filter_by_no_assignee?
     # Assignee_id takes precedence over assignee_username
-    params[:assignee_id].to_s == NONE || params[:assignee_username].to_s == NONE
+    [NONE, FILTER_NONE].include?(params[:assignee_id].to_s.downcase) || params[:assignee_username].to_s == NONE
+  end
+
+  def filter_by_any_assignee?
+    params[:assignee_id].to_s.downcase == FILTER_ANY
   end
 
   # rubocop: disable CodeReuse/ActiveRecord
@@ -399,15 +408,17 @@ def sort(items)
 
   # rubocop: disable CodeReuse/ActiveRecord
   def by_assignee(items)
-    if assignee
-      items = items.where(assignee_id: assignee.id)
-    elsif no_assignee?
-      items = items.where(assignee_id: nil)
+    if filter_by_no_assignee?
+      items.where(assignee_id: nil)
+    elsif filter_by_any_assignee?
+      items.where('assignee_id IS NOT NULL')
+    elsif assignee
+      items.where(assignee_id: assignee.id)
     elsif assignee_id? || assignee_username? # assignee not found
-      items = items.none
+      items.none
+    else
+      items
     end
-
-    items
   end
   # rubocop: enable CodeReuse/ActiveRecord