Add one-shot ECB methods

Add one-shot ECB methods

This change adds SymmetricAlgorithm.EncryptEcb, SymmetricAlgorithm.DecryptEcb, their
respective Try- and -Core methods, derived type implementations thereof, and tests.

There's an open question of should these members on on the base class throw or
"succeed if the Mode property is in agreement with the algorithm".  While the latter is "nicer",
just throwing  is easier to reason about, and that's the current behavior.

Co-authored-by: Jeremy Barton <jbarton@microsoft.com>