Custom fields which start with a number can break views

Problem/Motivation

If you add a custom field to an entity type supported by views and the field starts with a number then \Drupal\views\Plugin\views\PluginBase::viewsTokenReplace() will fail it's assertions if you rewrite the output of a field. This because the field starts with a number and fails this regex:

assert(preg_match('/^[a-zA-Z_\x7f-\xff][a-zA-Z0-9_\x7f-\xff]*$/', $token) === 1, 'Tokens need to be valid Twig variables.');

Steps to reproduce

Note this can only occur on base fields as configurable fields will error - see \Drupal\field\Entity\FieldStorageConfig::__construct()

See test added by MR.

Proposed resolution

Either fix views... or deprecate base fields with such names... but renaming base fields for existing sites is not that easy.

Current solution fixes views.

Remaining tasks

User interface changes

None

Introduced terminology

N/a

API changes

None

Data model changes

None

Release notes snippet

N/a