refactor: use the term unmount instead of dismount (#1478)

* refactor: use UNMOUNT instead of DISMOUNT in code

This change updates the term DISMOUNT in constants to UNMOUNT.
Other occurrences (e.g. variable names) are left alone for now.

* refactor(ui): use unmount instead of dismount

This change updates the GUI text and replaces dismount with unmount.

* docs: update term dismount -> unmount

* refactor(cmdline): add unmount

This change adds an argument 'unmount' for command line usage, while
trying to deprecate the old disnount argument.
The current dismount argument/flag will still work to not introduce
a breaking change.

* docs: mention that /dismount is deprecated

This change fixes the shorthand version of the argument /unmount
It also adds back the info for /dismount and that it is deprecated.

src/Common/Dlgcode.c

@@ -8220,7 +8220,7 @@ int DriverUnmountVolume (HWND hwndDlg, int nDosDriveNo, BOOL forced)
 	unmount.nDosDriveNo = nDosDriveNo;
 	unmount.ignoreOpenFiles = forced;
 
-	bResult = DeviceIoControl (hDriver, TC_IOCTL_DISMOUNT_VOLUME, &unmount,
+	bResult = DeviceIoControl (hDriver, TC_IOCTL_UNMOUNT_VOLUME, &unmount,
 			sizeof (unmount), &unmount, sizeof (unmount), &dwResult, NULL);
 
 	if (bResult == FALSE)
@@ -15984,4 +15984,4 @@ cleanup:
 
 	return result;
 }
-#endif
+#endif