Swallow bundler exceptions when running tests

Let's avoid useless output when testing stuff related to Bundler.
Create Changing Columns on migrations guides

[ci skip]
Add Total of grouped items to AR query interface on guides

[ci skip]
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
Merge pull request #15435 from sgrif/sg-rm-serialization

Remove most code related to serialized properties
Merge pull request #15459 from maurogeorge/add-total-grouped-items

Add Total of grouped items to Active Record query interface on guides [ci skip]
Remove docs regarding grouping multiple values, as we should avoid
duplicating API reference in guides. Also :scissors: [ci skip]
Merge pull request #15457 from maurogeorge/add-changing-columns

Create Changing Columns on migrations guides [ci skip]
:nail_care: for migrations guide from #15457 [ci skip]
New records should remain new after yaml serialization
Merge pull request #15444 from sgrif/sg-yaml-new-record

New records should remain new after yaml serialization
Feature requests should be made on the mailing list, not submitted to
the issue tracker. See also #15455 [ci skip]