Add ActiveRecord::Base#previously_persisted?

Returns `true` if the object has been previously persisted but now it has been deleted.

This is a follow up of https://github.com/rails/rails/pull/42256/files#r641914920

activerecord/CHANGELOG.md

@@ -1,3 +1,7 @@
+*   Add `ActiveRecord::Base#previously_persisted?`
+
+    Returns `true` if the object has been previously persisted but now it has been deleted.
+
 *   Deprecate `partial_writes` in favor of `partial_inserts` and `partial_updates`.
 
     This allows to have a different behavior on update and create.

activerecord/lib/active_record/persistence.rb

@@ -467,6 +467,11 @@ module ActiveRecord
       @previously_new_record
     end
 
+    # Returns true if this object was previously persisted but now it has been deleted.
+    def previously_persisted?
+      !new_record? && destroyed?
+    end
+
     # Returns true if this object has been destroyed, otherwise returns false.
     def destroyed?
       @destroyed

activerecord/test/cases/base_test.rb

@@ -800,6 +800,14 @@ class BasicsTest < ActiveRecord::TestCase
     assert_equal false, Topic.find(1).previously_new_record?
   end
 
+  def test_previously_persisted_returns_boolean
+    assert_equal false, Topic.new.previously_persisted?
+    assert_equal false, Topic.new.destroy.previously_persisted?
+    assert_equal false, Topic.first.previously_persisted?
+    assert_equal true, Topic.first.destroy.previously_persisted?
+    assert_equal true, Topic.first.delete.previously_persisted?
+  end
+
   def test_dup
     topic = Topic.find(1)
     duped_topic = nil

activerecord/test/cases/clone_test.rb

@@ -14,6 +14,7 @@ module ActiveRecord
       assert cloned.persisted?, "topic persisted"
       assert_not cloned.new_record?, "topic is not new"
       assert_not cloned.previously_new_record?, "topic was not previously new"
+      assert_not cloned.previously_persisted?, "topic was not previously persisted"
     end
 
     def test_stays_frozen

activestorage/app/models/active_storage/blob.rb

@@ -293,9 +293,8 @@ class ActiveStorage::Blob < ActiveStorage::Record
   # blobs. Note, though, that deleting the file off the service will initiate an HTTP connection to the service, which may
   # be slow or prevented, so you should not use this method inside a transaction or in callbacks. Use #purge_later instead.
   def purge
-    previously_persisted = persisted?
     destroy
-    delete if previously_persisted
+    delete if previously_persisted?
   rescue ActiveRecord::InvalidForeignKey
   end