[10/10] gdiplus: Filter tabs out until they are properly supported using stringformat.

[Vincent Povirk]

This should probably be handled somehow by gdip_format_string.
DrawDriverString doesn't have access to the StringFormat, and there's
a good change that the native implementation really does draw tabs as
squares. Also, MeasureCharacterRanges and MeasureString will have to
account for tabstops.

gdip_format_string already has logic to ignore certain characters, but
it needs more thought as to how we can do that and keep the offsets
passed to the callback accurate, and how to eventually pass
information about tabs to the callback.

If this does turn out to be a correct change for DrawDriverString (I
predict that it is not), then MeasureDriverString should be updated as
well.