tdf#126533 docx export: page background vml fill: tiles/patterns

This patch only benefits LO. MSO ignores "frame" and always
treats page background as it if were tiled,
but that is a trait we do NOT want to mimic.

Textures are the primary fill type that needs to be tiled
(instead of scaled/stretched).

LO export also treats patterns as tiled bitmaps,
and the end result of exporting as a tile looks the same
as the original pattern.
It just loses HOW the page background (i.e. as a pattern)
but that is very low value. It is rather difficult
to export as a true pattern and just not worth the effort
of identifying the correct fore/background colors,
converting to b&w image, and inverting the B&W image
if the first pixel is white instead of black.

[Hatching seems similar to patterns,
but rarely (and only coincidentally) would it tile well.
I think hatching is a new DML-only thing.
Hatching is not in the page background UI of MS Word.
LO just exports any hatching as a solid color.]

Change-Id: I5cd3f1c6e380edb5e5b21900bad289fa298574e2
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/163206
Tested-by: Jenkins
Reviewed-by: Justin Luth <jluth@mail.com>

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