Fix email auto link when there are two chars in local part

Email auto linking used to accept either a single char or more than 2
chars in the local part. Updated the regular expression to accept 1 or
more chars.

Test: added test to cts.LinkifyTest
Test: bit -t CtsTextTestCases:android.text.util.cts.LinkifyTest
Test: bit -t FrameworksCoreTests:android.util.PatternsTest
Test: bit -t FrameworksCoreTests:android.text.util.LinkifyTest
Test: bit -t CtsWidgetTestCases:android.widget.cts.TextViewTest

Bug: 64467661
Change-Id: I4e28a344ff1bc50da353b9490eaaec99a751bffb