for #25713: 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 Toolkit, 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. All other signals are emitted as expected from Hiero.