Revamp post filtering system (#18058)

* Add model for custom filter keywords

* Use CustomFilterKeyword internally

Does not change the API

* Fix /filters/edit and /filters/new

* Add migration tests

* Remove whole_word column from custom_filters (covered by custom_filter_keywords)

* Redesign /filters

Instead of a list, present a card that displays more information and handles
multiple keywords per filter.

* Redesign /filters/new and /filters/edit to add and remove keywords

This adds a new gem dependency: cocoon, as well as a npm dependency:
cocoon-js-vanilla. Those are used to easily populate and remove form fields
from the user interface when manipulating multiple keyword filters at once.

* Add /api/v2/filters to edit filter with multiple keywords

Entities:
- `Filter`: `id`, `title`, `filter_action` (either `hide` or `warn`), `context`
  `keywords`
- `FilterKeyword`: `id`, `keyword`, `whole_word`

API endpoits:
- `GET /api/v2/filters` to list filters (including keywords)
- `POST /api/v2/filters` to create a new filter
  `keywords_attributes` can also be passed to create keywords in one request
- `GET /api/v2/filters/:id` to read a particular filter
- `PUT /api/v2/filters/:id` to update a new filter
  `keywords_attributes` can also be passed to edit, delete or add keywords in
   one request
- `DELETE /api/v2/filters/:id` to delete a particular filter
- `GET /api/v2/filters/:id/keywords` to list keywords for a filter
- `POST /api/v2/filters/:filter_id/keywords/:id` to add a new keyword to a
   filter
- `GET /api/v2/filter_keywords/:id` to read a particular keyword
- `PUT /api/v2/filter_keywords/:id` to edit a particular keyword
- `DELETE /api/v2/filter_keywords/:id` to delete a particular keyword

* Change from `irreversible` boolean to `action` enum

* Remove irrelevent `irreversible_must_be_within_context` check

* Fix /filters/new and /filters/edit with update for filter_action

* Fix Rubocop/Codeclimate complaining about task names

* Refactor FeedManager#phrase_filtered?

This moves regexp building and filter caching to the `CustomFilter` class.

This does not change the functional behavior yet, but this changes how the
cache is built, doing per-custom_filter regexps so that filters can be matched
independently, while still offering caching.

* Perform server-side filtering and output result in REST API

* Fix numerous filters_changed events being sent when editing multiple keywords at once

* Add some tests

* Use the new API in the WebUI

- use client-side logic for filters we have fetched rules for.
  This is so that filter changes can be retroactively applied without
  reloading the UI.
- use server-side logic for filters we haven't fetched rules for yet
  (e.g. network error, or initial timeline loading)

* Minor optimizations and refactoring

* Perform server-side filtering on the streaming server

* Change the wording of filter action labels

* Fix issues pointed out by linter

* Change design of “Show anyway” link in accordence to review comments

* Drop “irreversible” filtering behavior

* Move /api/v2/filter_keywords to /api/v1/filters/keywords

* Rename `filter_results` attribute to `filtered`

* Rename REST::LegacyFilterSerializer to REST::V1::FilterSerializer

* Fix systemChannelId value in streaming server

* Simplify code by removing client-side filtering code

The simplifcation comes at a cost though: filters aren't retroactively
applied anymore.

app/javascript/mastodon/actions/notifications.js

@@ -12,10 +12,8 @@ import { saveSettings } from './settings';
 import { defineMessages } from 'react-intl';
 import { List as ImmutableList } from 'immutable';
 import { unescapeHTML } from '../utils/html';
-import { getFiltersRegex } from '../selectors';
 import { usePendingItems as preferPendingItems } from 'mastodon/initial_state';
 import compareId from 'mastodon/compare_id';
-import { searchTextFromRawStatus } from 'mastodon/actions/importer/normalizer';
 import { requestNotificationPermission } from '../utils/notifications';
 
 export const NOTIFICATIONS_UPDATE      = 'NOTIFICATIONS_UPDATE';
@@ -62,20 +60,17 @@ export function updateNotifications(notification, intlMessages, intlLocale) {
     const showInColumn = activeFilter === 'all' ? getState().getIn(['settings', 'notifications', 'shows', notification.type], true) : activeFilter === notification.type;
     const showAlert    = getState().getIn(['settings', 'notifications', 'alerts', notification.type], true);
     const playSound    = getState().getIn(['settings', 'notifications', 'sounds', notification.type], true);
-    const filters      = getFiltersRegex(getState(), { contextType: 'notifications' });
 
     let filtered = false;
 
-    if (['mention', 'status'].includes(notification.type)) {
-      const dropRegex   = filters[0];
-      const regex       = filters[1];
-      const searchIndex = searchTextFromRawStatus(notification.status);
+    if (['mention', 'status'].includes(notification.type) && notification.status.filtered) {
+      const filters = notification.status.filtered.filter(result => result.filter.context.includes('notifications'));
 
-      if (dropRegex && dropRegex.test(searchIndex)) {
+      if (filters.some(result => result.filter.filter_action === 'hide')) {
         return;
       }
 
-      filtered = regex && regex.test(searchIndex);
+      filtered = filters.length > 0;
     }
 
     if (['follow_request'].includes(notification.type)) {