* Add failing tests for issues with wrapped values where the value is the default

* Add test for wrapped values without a value set

* Bugfix for wrapper types with default values.

The previous optimizations for wrapper types had a bug that prevented
wrappers from registering as "present" if the "value" field was not
present on the wire.

In practice the "value" field will not be serialized when it is zero,
according to proto3 semantics, but due to the optimization this
prevented it from creating a new object to represent the presence of the
field.

The fix is to ensure that if the wrapper message is present on the wire,
we always initialize its value to zero.
Co-authored-by: Joshua Haberman <jhaberman@gmail.com>
Co-authored-by: Dan Quan <dan@quan.io>