Make workspace (project) & session xml setting files consistent while their file extensions are defined in Preferences dialog:
1. If I specify a session file in the command line (, or if I double-click a session file in the Explorer), not the session file itself is opened, but the session stored in it.
2. If I specify a workspace file in the command line (, or if I double-click a workspace file in the Explorer), not the workspace file itself is opened, but the Project Panel 1 switches to the specified workspace file.
3. If I specify a session file in the `File` menu `Open Ctrl-O`, not the session file itself is opened, but the session stored in it.
4. If I specify a workspace file in the `File` menu `Open Ctrl-O`, not the workspace file itself is opened, but the Project Panel 1 switches to the specified workspace file.
5. If I drag a session file to Npp, not the session file itself is opened, but the session stored in it.
6. If I drag a workspace file to Npp, not the workspace file itself is opened, but the Project Panel 1 switches to the specified workspace file.
That means that once an user extension is defined for these 2 types of file, Notepad++ stores only the session or the workspace but not opens the file itself. The session and workspace setting files are not supposed to be edited manually.
If a defined conflict happens (for example, a non session or workspace setting file with the defined extension), user can always remove the defined extension from Preferences dialog temporarily to open it.
cherry picked from commit 70e746b7a8fe44c9a1e724581ceb3b457138a474
Close#8374, fix#8324
87dc9cc5d2