Proposal: NumberBox Placeholder Features

## Summary
The NumberBox sould have the PlaceholderForeground Property.
It should be an option to add an red (asterisk) to the PlaceholderText property (and Header property) to show it as a Required field.
, and if the focus lose without filling in the field it should show a red message under the TextBox 'Please enter a valid {PlaceholderText}',
it can be added the feature of specifying the type of the textbox, for example, Type='Email', so if the text inside the TextBox isnt in the format of an email it should show the red message too. and if some fields are not filled out the Submit button should not work, and it should show a message with the problem.

## Rationale
* As the TextBox and ComboBox have the PlaceholderForeground property it will be appreciated if all controls will have the same design and look.
* It will be much easier for developers who develops Kiosk stations where users need to sign up or fill in forms to indicate what is a required field.

## Important Notes
public bool RequiredField { get; set; }

public enum Type
{
Address,
Email,
PostCode,
Currency // with local culture
Submit, // for Button
etc.
}

public Type TextType { get; set; }

Review NumberBox alongside the existing TextBox and ComboBox behavior, especially PlaceholderForeground and validation-related expectations. Clarify which subset of required-field indicators, validation messages, text types, and submit behavior is intended before identifying implementation and test locations; done should include an agreed scope and coverage for the selected behavior.

Written by the indexing model from the issue text.