Add wxFileType::GetExpandedCommand()

This new method allows to get the command expanded with the given file name
for commands other than "Open" and "Print".

Closes #17367.

docs/changes.txt

@@ -61,6 +61,7 @@ All:
   functions. See wxGetOsVersion(), wxPlatformInfo, and wxAppTraits.
 - wxLogInfo() now logs messages if the log level is high enough, even without
   wxLog::SetVerbose() which now only affects wxLogVerbose().
+- Add wxFileType::GetExpandedCommand() (troelsk).
 
 wxMSW: