Change CT/CG text rendering to default on DWRITE_RENDERING/MEASURING_…

[ms-jihua]

…MODE_GDI_NATURAL

Fixes #1594

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This change is 

[ms-jihua]

I tried a few different rendering modes. The GDI modes were the only ones that actually fixed the problem while not introducing noticeable aliasing to other test apps like iLabyrinth. Between GDI_CLASSIC and GDI_NATURAL, there was not very much noticeable difference, but GDI_NATURAL seemed to look slightly better? (very scientific)

[rajsesh]

I am convinced that this is the right approach to fix this specific bug. Our default rendering mode should be default, as that would let DWrite pick the right rendering mode. GDI, GDI natural, etc are anti-aliased in the horizontal direction, and according to the documentation large fonts will not look good (they should use the DWRITE_RENDERING_MODE_NATURAL_SYMMETRIC mode).

The issue here per our offline discussion is:

1. App is drawing to smaller bitmap and scaling it. Without anti-aliasing, this app will look okay because it is pixelated overall, but that is not a good solution.

2. Things like sub pixel positioning will be lost. Those are clear winners on phone (small screen devices).

[ms-jihua]

We decided that this solution was not satisfactory - going to investigate another one.