Entity Display modes form allows to create machine names including dots

This bug is due to the replace_pattern is modified to [^a-z0-9_.]+ in EntityDisplayModeAddForm to allow the dot included with the prefix eg: "node.".

This change is necessary to pass this validation when editing or deleting the display mode, however this change allow to enter extra dots in the machine name during entity creation.

To avoid this, this patch puts the default value again in Display mode creation form, in this way, user can't add dots in the entity add form, but included dot is allowed when the entity is edited or deleted.

Other way could be create a more complex regex which validates both cases. I tried it, but I was not able to reach it. Maybe someone with more experience could afford it.

Regards.

Patch in #4 does not work because is necessary allow dots for editing and deleting display modes.

If you test it manually, you'll get the following message in those cases:

The machine-readable name must contain only lowercase letters, numbers, and underscores.

Because the display mode machine_name is entity_type.your_machine_name

Regards.

New patch addind tests to approach in #1

Re-rolling

Re-rolling