Fix #26962: Retaining user info in user edit after submit

[yashyadav-mo]

Core Track Ticket: https://core.trac.wordpress.org/ticket/26962

Problem
When updating a user on wp-admin/profile.php or wp-admin/user-edit.php, any validation error causes the form to be rebuilt from stored database values. As a result, valid changes entered in other fields are lost from the screen after reload, forcing the user to re-enter them.

This is inconsistent with the Add New User flow in wp-admin/user-new.php, which preserves submitted values after an error.

Root Cause
wp-admin/user-edit.php calls edit_user( $user_id ) on submit. If that returns WP_Error, the page falls through to rendering and rebuilds form state with get_user_to_edit( $user_id ).

get_user_to_edit() only loads persisted user data from the database, so it has no knowledge of the submitted $_POST values from the failed request. That means the form loses the user's unsaved but valid input.

An earlier approach tried to partially save valid fields even when validation failed, but that changes database state during an error path and conflicts with existing edit_user() behavior and PHPUnit expectations.

Solution
This PR keeps edit_user() non-persisting on validation failure and fixes the problem at the form-rendering layer instead.

It introduces a helper in wp-admin/includes/user.php that:

Starts from get_user_to_edit( $user_id )
Overlays safe submitted values from $_POST onto the returned WP_User object
Excludes fields that failed validation based on WP_Error metadata and known username/password-related error codes
Never repopulates password fields
wp-admin/user-edit.php now uses that helper when rerendering the form after a failed update, so valid submitted values remain visible without being written to the database.

The implementation also handles option-backed controls used by the profile form, such as:

administration color scheme
toolbar preference
other personal option toggles
This preserves the user’s submitted state on error while keeping database data unchanged until validation succeeds.

[github-actions]

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[github-actions]

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[github-actions]

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