Swallow bundler exceptions when running tests

Let's avoid useless output when testing stuff related to Bundler.
Merge pull request #14881 from robin850/patch-19

Swallow bundler exceptions when running tests
Don't change values in `@raw_attributes` during serialization

During `init_with`, the attributes given to the coder will be placed
into `@raw_attributes`. As such, we should read from `@raw_attributes`
when encoding, rather than `@attributes`, which has been type cast.
Merge pull request #15432 from sgrif/sg-coder-type-casting

Don't change values in `@raw_attributes` during serialization
Remove most code related to serialized properties

Nearly completely implemented in terms of custom properties.
`_before_type_cast` now stores the raw serialized string consistently,
which removes the need to keep track of "state". The following is now
consistently true:

- `model.serialized == model.reload.serialized`
- A model can be dumped and loaded infinitely without changing
- A model can be saved and reloaded infinitely without changing