Wording optimization in select widget

Problem/Motivation

When using the select list widget, this module adds a "- None -" value as first option.
Since the field is required, the text should rather be "- Select a value -", which is what is used in Core for select lists with required fiields.
Also, the text should be translatable.

Steps to reproduce

1. Create a Views Reference field in a node type of your choice and allow more than one view to be selected.
2. Choose the select list widget in the entity form.
3. Create a new node of that type.
4. The select list is displayed with "- None -" as the first option.
5. When using a language other than English, the option still reads "- None -".

Proposed resolution

Change the text to "- Select a value -" and make it translatable.

Remaining tasks

Write patch.

User interface changes

See above.

API changes

None.

Data model changes

None.