Case insensitive signup (#5634)

* Always delete data after each, even for mongo.

* Add failing simple case test

* run all tests

* 1. when validating username be case insensitive

2. add _auth_data_anonymous to specialQueryKeys...whatever that is!

* More case sensitivity

1. also make email validation case insensitive
2. update comments to reflect what this change does

* wordsmithery and grammar

* first pass at a preformant case insensitive query.  mongo only so far.

* change name of parameter from insensitive to
caseInsensitive

* Postgres support

* properly handle auth data null

* wip

* use 'caseInsensitive' instead of 'insensitive' in all places.

* update commenet to reclect current plan

* skip the mystery test for now

* create case insensitive indecies for
mongo to support case insensitive
checks for email and username

* remove unneeded specialKey

* pull collation out to a function.

* not sure what i planned
to do with this test.
removing.

* remove typo

* remove another unused flag

* maintain order

* maintain order of params

* boil the ocean on param sequence
i like having explain last cause it seems
like something you would
change/remove after getting what you want
from the explain?

* add test to verify creation
and use of caseInsensitive index

* add no op func to prostgress

* get collation object from mongocollection
make flow lint happy by declaring things Object.

* fix typo

* add changelog

* kick travis

* properly reference static method

* add a test to confirm that anonymous users with
unique username that do collide when compared
insensitively can still be created.

* minot doc nits

* add a few tests to make sure our spy is working as expected
wordsmith the changelog

Co-authored-by: Diamond Lewis <findlewis@gmail.com>

spec/MongoStorageAdapter.spec.js

@@ -318,6 +318,38 @@ describe_only_db('mongo')('MongoStorageAdapter', () => {
     );
   });
 
+  it('should use index for caseInsensitive query', async () => {
+    const user = new Parse.User();
+    user.set('username', 'Bugs');
+    user.set('password', 'Bunny');
+    await user.signUp();
+
+    const database = Config.get(Parse.applicationId).database;
+    const preIndexPlan = await database.find(
+      '_User',
+      { username: 'bugs' },
+      { caseInsensitive: true, explain: true }
+    );
+
+    const schema = await new Parse.Schema('_User').get();
+
+    await database.adapter.ensureIndex(
+      '_User',
+      schema,
+      ['username'],
+      'case_insensitive_username',
+      true
+    );
+
+    const postIndexPlan = await database.find(
+      '_User',
+      { username: 'bugs' },
+      { caseInsensitive: true, explain: true }
+    );
+    expect(preIndexPlan.executionStats.executionStages.stage).toBe('COLLSCAN');
+    expect(postIndexPlan.executionStats.executionStages.stage).toBe('FETCH');
+  });
+
   if (
     process.env.MONGODB_VERSION === '4.0.4' &&
     process.env.MONGODB_TOPOLOGY === 'replicaset' &&