Custom user entity forms crash when module is enabled if username or email is not on the form

Problem/Motivation

When rendering a custom form for an existing user without the username or email fields it still alters the form and effectively adds the name in but with just type=>value and it then tries to save a null against the user and crashes.

Steps to reproduce

Create new view mode for user entity
Only add as an example, a custom field on it, such as address
Create custom form route to display user with that new form view mode
Attempt to save the form
SQLSTATE[23000]: Integrity constraint violation: 1048 Column 'name' cannot be null

Proposed resolution

Only adjust form elements that exist in the entity form

Remaining tasks

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User interface changes

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API changes

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Data model changes

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