Add ConfigSchemaChecker to development.services.yml

Updated the CR, updated the message to be more helpful and also show a link to the documentation. Tests seem green. Let's see if we can continue here.

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Removed new forbidden word "please" from the message.

1 small comment but

Consider adding a todo to move it out of the Testing namespace in D9.

And decide on the namespace. There was an initial suggestion of 'Drupal\Core\Config\Schema\ConfigSchemaChecker'. And later the patch used '\Drupal\Core\Config\Devel\ConfigSchemaChecker', which was changed to '\Drupal\Core\Config\Development\ConfigSchemaChecker'.

Is the current namespace '\Drupal\Core\Config\Development\ConfigSchemaChecker' the one to use or something else?

Is the todo still needed?

Has the namespace been decided?

Added a couple small grammar suggestions.

We can decide the namespace, i think this placement is all good.

Applied suggestion for grammar and adjusted contructor.

+1 from me.

Nit: add readonly to the promoted properties. Otherwise can RTBC.

Yeah, might as well, good one.

There are test failures. Might need rerunning?

Re-run seemed to do the trick. Believe all feedback has been addressed

The CR is no longer correct as the class is not moving. I do think that the CR should exist - it should detail that by default if you use the development.services.yml you will can warnings when saving configuration that does not comply with schema. Once the CR is updated this can be set back to RTBC. The solution looks elegant and it's great that this emits warnings rather than errors.

CR has been updated.

CR looks great.

Committed 733dc5f and pushed to 11.x. Thanks!