Add open personal scripts to solutions and clarify the Scripts menu

Organise the Scripts menu into clear groups for creating and opening scripts, adding them to a solution, running the current script, using personal scripts, and managing shortcuts. Provide explicit Run Personal Script and Edit Personal Script submenus.

Add an Add Current Script to Solution command that takes the current personal script's editor contents, including unsaved edits, asks for a name, and makes the open tab part of the solution. The original personal file is preserved. The action supports Undo and Redo and works before the solution has been saved.