for #25173: manually emit kBeforeProjectLoad signal since Hiero doesn't

Hiero has a bunch of signals it emits when certain actions take place. This includes a signal emitted both before and after a project is loaded. When loading through the Toolkit File Manager, Hiero doesn't emit the `kBeforeProjectLoad` signal (presumably because there's no way to know a project is about to be loaded when done this way?) 

This emits the signal manually immediately prior to the opening of the project.