FEATURE: Promote bookmarks with reminders to core functionality (#9369)

The main thrust of this PR is to take all the conditional checks based on the `enable_bookmarks_with_reminders` away and only keep the code from the `true` path, making bookmarks with reminders the core bookmarks feature. There is also a migration to create `Bookmark` records out of `PostAction` bookmarks for a site.

### Summary

* Remove logic based on whether enable_bookmarks_with_reminders is true. This site setting is now obsolete, the old bookmark functionality is being removed. Retain the setting and set the value to `true` in a migration.
* Use the code from the rake task to create a database migration that creates bookmarks from post actions.
* Change the bookmark report to read from the new table.
* Get rid of old endpoints for bookmarks
* Link to the new bookmarks list from the user summary page

db/migrate/20200409033412_create_bookmarks_from_post_action_bookmarks.rb

@@ -0,0 +1,58 @@
+# frozen_string_literal: true
+
+class CreateBookmarksFromPostActionBookmarks < ActiveRecord::Migration[6.0]
+  def up
+    SiteSetting.enable_bookmarks_with_reminders = true
+
+    bookmarks_to_create = []
+    loop do
+      # post action type id 1 is :bookmark. we do not need to OFFSET here for
+      # paging because the WHERE bookmarks.id IS NULL clause handles this effectively,
+      # because we do not get bookmarks back that have already been inserted
+      post_action_bookmarks = DB.query(
+        <<~SQL, type_id: 1
+        SELECT post_actions.id, post_actions.post_id, posts.topic_id, post_actions.user_id
+        FROM post_actions
+        INNER JOIN posts ON posts.id = post_actions.post_id
+        LEFT JOIN bookmarks ON bookmarks.post_id = post_actions.post_id AND bookmarks.user_id = post_actions.user_id
+        INNER JOIN topics ON topics.id = posts.topic_id
+        WHERE bookmarks.id IS NULL AND post_action_type_id = :type_id AND post_actions.deleted_at IS NULL AND posts.deleted_at IS NULL
+        LIMIT 2000
+        SQL
+      )
+      break if post_action_bookmarks.count.zero?
+
+      post_action_bookmarks.each do |pab|
+        now = Time.zone.now
+        bookmarks_to_create << "(#{pab.topic_id}, #{pab.post_id}, #{pab.user_id}, '#{now}', '#{now}')"
+      end
+
+      create_bookmarks(bookmarks_to_create)
+      bookmarks_to_create = []
+    end # loop
+  end
+
+  def down
+    raise ActiveRecord::IrreversibleMigration
+  end
+
+  def create_bookmarks(bookmarks_to_create)
+    return if bookmarks_to_create.empty?
+
+    # this will ignore conflicts in the bookmarks table so
+    # if the user already has a post bookmarked in the new way,
+    # then we don't error and keep on truckin'
+    #
+    # we shouldn't have duplicates here at any rate because of
+    # the above LEFT JOIN but best to be safe knowing this
+    # won't blow up
+    #
+    DB.exec(
+      <<~SQL
+      INSERT INTO bookmarks (topic_id, post_id, user_id, created_at, updated_at)
+      VALUES #{bookmarks_to_create.join(",\n")}
+      ON CONFLICT DO NOTHING
+      SQL
+    )
+  end
+end