Keyword/phrase filtering (#7905)

* Add keyword filtering

    GET|POST       /api/v1/filters
    GET|PUT|DELETE /api/v1/filters/:id

- Irreversible filters can drop toots from home or notifications
- Other filters can hide toots through the client app
- Filters use a phrase valid in particular contexts, expiration

* Make sure expired filters don't get applied client-side

* Add missing API methods

* Remove "regex filter" from column settings

* Add tests

* Add test for FeedManager

* Add CustomFilter test

* Add UI for managing filters

* Add streaming API event to allow syncing filters

* Fix tests

app/controllers/api/v1/filters_controller.rb

@@ -0,0 +1,48 @@
+# frozen_string_literal: true
+
+class Api::V1::FiltersController < Api::BaseController
+  before_action -> { doorkeeper_authorize! :read }, only: [:index, :show]
+  before_action -> { doorkeeper_authorize! :write }, except: [:index, :show]
+  before_action :require_user!
+  before_action :set_filters, only: :index
+  before_action :set_filter, only: [:show, :update, :destroy]
+
+  respond_to :json
+
+  def index
+    render json: @filters, each_serializer: REST::FilterSerializer
+  end
+
+  def create
+    @filter = current_account.custom_filters.create!(resource_params)
+    render json: @filter, serializer: REST::FilterSerializer
+  end
+
+  def show
+    render json: @filter, serializer: REST::FilterSerializer
+  end
+
+  def update
+    @filter.update!(resource_params)
+    render json: @filter, serializer: REST::FilterSerializer
+  end
+
+  def destroy
+    @filter.destroy!
+    render_empty
+  end
+
+  private
+
+  def set_filters
+    @filters = current_account.custom_filters
+  end
+
+  def set_filter
+    @filter = current_account.custom_filters.find(params[:id])
+  end
+
+  def resource_params
+    params.permit(:phrase, :expires_at, :irreversible, context: [])
+  end
+end