Add Client Script: Mandatory Field Highlighter with red border

[Rajat32-op]

PR Description:

• Highlights empty mandatory fields with error messages
• Uses g_form.showFieldMsg() and hideFieldMsg() instead of DOM manipulation
• Includes onLoad script for initial highlighting
• Includes onChange script for real-time updates
• Follows ServiceNow best practices and official APIs

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[ivan-betev]

Thank you for your contribution. You are almost there.

From the use case I see that fields required to be mandatory will be highlighted onLoad with a field message.

However in case of onChange it will always require a separate client script for each field to monitor the behavior. That doesn't make much sense for such a tiny function.

Either remove onChange or find a better way.