Add support for *.code-workspace mimetype

Support for opening *.code-workspace files in visual-studio-code
on Linux was added in https://github.com/microsoft/vscode/pull/95637.
However, it only supports deb and rpm files. This commit adds
appropriate files to register *.code-workspace as a separate mimetype
and opens them in visual-studio-code.

visual-studio-code.desktop

@@ -8,7 +8,7 @@ Type=Application
 StartupNotify=false
 StartupWMClass=code
 Categories=Utility;TextEditor;Development;IDE;
-MimeType=text/plain;inode/directory;
+MimeType=text/plain;inode/directory;application/x-visual-studio-code-workspace;
 Actions=new-empty-window;
 Keywords=vscode;