Changed dataset methods that take a Pattern filter to accept null.

In this case, null means the field should not be filterable, which is useful
in the cases where it represents a non-authenticated value like a password.

Test: atest CtsAutoFillServiceTestCases:LoginActivityTest#filterTextDisabledUsingNullRegex
Test: atest CtsAutoFillServiceTestCases:LoginActivityTest

Bug: 71359055
Fixes: 72711778

Change-Id: Idc8248f6c95fdb50b934840689616e42ddd6378c