This avoids a lot of mismatches between nsAString and char16_t*, thus removing
many getter_Copies() and ToNewUnicode() and get() calls, and generally making
things simpler.
Note: the patch removes GetDefaultPrinterNameFromGlobalPrinters() by simply
inlining it at its two callsites, which is easy with the changed types.
This also holds the resolution in the print settings, so that we can start to
remove the access to the native Windows print devices in the child process.
