Upstream already got FPDFPageObj_GetFillColor() and
FPDFPageObj_GetStrokeColor(), so what was necessary is just a
FPDFText_GetTextRenderMode() to find out which one to use.

Change-Id: I2f31fcadee8a4377b890e01ea62ed96bce275f2b
Reviewed-on: https://gerrit.libreoffice.org/58381Reviewed-by: Miklos Vajna <vmiklos@collabora.co.uk>
Tested-by: Jenkins