WASM: Upgrade the WASM PVM when migrating to proto alpha

Context

Prior to this patch, only newly originated smart rollups would benefit
from improvements brought by a new protocol. Now, when the WASM PVM
receives a `Protocol_migration` internal messages, it decodes its
payload in order to check if it needs to upgrade to a new revision.

This way, already existing smart rollups can benefit from new features
and improvements added in a more recent protocol.

This patch also introduces a test to check the consistency between the
naming scheme of the protocols, which have to be defined in two
places: `proto_*/lib_protocol/raw_context.ml` and
`lib_scoru_wasm/constants.ml`. Some instructions to update the test
when a new protocol is snapshot are also provided, to make the life of
developers doing the snapshot easier.

Manually testing the MR

Checklist

• Document the interface of any function added or modified (see the coding guidelines)
• Document any change to the user interface, including configuration parameters (see node configuration)
• Provide automatic testing (see the testing guide).
• For new features and bug fixes, add an item in the appropriate changelog (docs/protocols/alpha.rst for the protocol and the environment, CHANGES.rst at the root of the repository for everything else).
• Select suitable reviewers using the Reviewers field below.
• Select as Assignee the next person who should take action on that MR