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.
CompareCacheHashEntry::mCrit[] is the only case where the nsXPIDLString-ness
was important. The patch adds an explicit SetIsVoid() call to that class's
constructor and changes some null checks to IsVoid() checks.
This also corrects what I think are long standing issues with the mapping to and
from print settings on Windows.
Firstly it only uses the DEVMODE flags to decide what should get stored, in the
old code if paper size was not set, it would then use that possibly invalid
paper size to map to length and width. Paper setting prefs are mapped back if
they were stored or if they have been manually set to something sane.
Secondly it corrects the calculation that was used to convert from millimeters
to tenths of millimeters.
It also gets rid of the paperSizeType field, which was only used on Windows and
doesn't actually make sense according to the DEVMODE documentation as the
dmPaperLength and dmPaperWidth fields override the dmPaperSize, but can in
theory be specified at the same time.
