Added possibility to set backend locale per every admin user

[fballiano]

This PR adds the possibility to set a locale for the backend for every backend user, adding a column to the admin_user table and the UI components to use this new column.

This is the new field added to the "System -> My Account" form:

Manual testing scenarios (*)

1. login to the backend
2. click "system -> my account"
3. set the backend locale using the new field
4. save
5. logout
6. login to the backend again
7. the locale of the backend should be the one selected

[fballiano]

PHPStan fails for unrelated issues with the 20.0 branch

[luigifab]

No tested, but is there the possibility to leave the field empty?

[fballiano]

@luigifab there is

[elidrissidev]

Have you thought about saving the locale in the extra field instead of a new column?

[fballiano]

@elidrissidev ah! noup, didn't even notice it existed. It's interesting. I guess it makes sense.

Is "extra" supposed to be used by the "system" or by normal developers? I ask this because I'm wondering if who manipulates the data in that field knows that some more stuff can be added by the core and that they should act accordingly.

[kiatng]

The extra field is to save the state in the System Configuration:

magento-lts/app/code/core/Mage/Adminhtml/controllers/System/ConfigController.php

Lines 305 to 329 in 24176a8

	/**
	* Save state of configuration field sets
	*
	* @param array $configState
	* @return bool
	*/
	protected function _saveState($configState = [])
	{
	$adminUser = Mage::getSingleton('admin/session')->getUser();
	if (is_array($configState)) {
	$extra = $adminUser->getExtra();
	if (!is_array($extra)) {
	$extra = [];
	}
	if (!isset($extra['configState'])) {
	$extra['configState'] = [];
	}
	foreach ($configState as $fieldset => $state) {
	$extra['configState'][$fieldset] = $state;
	}
	$adminUser->saveExtra($extra);
	}
	return true;
	}

So, if you use it, it may be overwritten on lines 322-325. Using it for locale is not what it is intended for. It's better with a new column.

[fballiano]

@kiatng thank you!

[elidrissidev]

I know it's used for user config state, but it's put inside array key configState to allow storing additional data in there. Anyways, adding a new column doesn't hurt :)

[m-overlund]

Tested without issues

The base branch was changed.

[fballiano]

I'm merging cause we have 1 green check and 1 gray check but 2 more gray checks were dismissed only cause of the branch change, without code change (and the branch is still v20 at the end of the day)