Show warning message before upgrading project formats

[dicksonlaw583]

Is your feature request related to a problem?

Ever since the project format started shifting in early 2024, I have been seeing an increase in GMC threads involving people who opened projects in a newer IDE version, decided to roll back, and then found out that the project is no longer compatible with the older IDE. Very often these are the same people who have neither backups nor source control to protect their projects, and they are now stuck with no easy way back. Many of these people think their project wouldn't change as long as they don't hit save, but experienced responders all know that the project changes as soon as it is opened, and right now it is happening silently and to the detriment of unprepared novices.

Describe the solution you'd like

Upon opening a project from an older IDE and/or project format, I would like this message to be shown:

This project was created by an older IDE and needs to be upgraded. How would you like to proceed?

3 options should be presented:

• Open as new project: Convert the project to the current IDE format as a new project (location selected with file selector window), and open the converted copy. Same as current behaviour when loading a pre-2.3 project.
• Convert project: Show a yes/no question asking "This will overwrite the current project. Please make sure that you have an existing backup or source control commit before continuing. Would you like to proceed?". If user clicks "Yes", convert the project to the current IDE format in-place, and open it.
• Cancel: Abort loading the project and return to the home screen.

Describe alternatives you've considered

Many GMC responders have been promoting the use of source control for years, but most of the time the novices just don't listen until they have already lost a major project. This is in the same spirit as #2859 --- protecting novices from common but often fatal mistakes.

Additional context

No response