normalizeEmail function
Canonicalizes an email address.
Lowercases the domain and, for Gmail addresses, lowercases the local
part, removes dots and strips any +tag suffix. Returns null if the
input is not a valid email address.
Example:
normalizeEmail('Test.User+tag@GMAIL.com'); // 'testuser@gmail.com'
normalizeEmail('User@Example.COM'); // 'User@example.com'
normalizeEmail('not-an-email'); // null
Implementation
String? normalizeEmail(String str) => _normalizeEmail(str);