Add unit tests for encodeData

The function `TypedDataUtils.encodeData` has been thoroughly tested
with all novel inputs I could think of. Each supported version (V3 and
V4) have been tested independently with each input. There are also
tests for each input that should have an identical encoding between
V3 and V4, and each that should have non-matching signatures..

The `encodeData` assertions that accompanied the signature tests have
been deleted, as they're now redundant.