Regression test for HttpsURLConnection.setSSLSocketFactory(null).

This invocation should throw IAE but didn't do so since at least
Android KitKat. A companion CL in this CL topic fixes the behavior.
This CL adds a test to guard against regressions.

Test: URLConnectionTest.testNullSSLSocketFactory_throws() fails
      before the companion CL but passes afterwards.
Bug: 73702052

Change-Id: Ibba0b89ead8a686104dad266d7fcfb29bb2f957b