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/helper.js

@@ -207,13 +207,7 @@ afterEach(function(done) {
         'There were open connections to the server left after the test finished'
       );
     }
-    on_db(
-      'postgres',
-      () => {
-        TestUtils.destroyAllDataPermanently(true).then(done, done);
-      },
-      done
-    );
+    TestUtils.destroyAllDataPermanently(true).then(done, done);
   };
   Parse.Cloud._removeAllHooks();
   databaseAdapter