evas: Implement support for different H/V font DPI

evas: Implement support for different H/V font DPI

This is modifying how a rarely used environment variable that sets the
DPI used for font sizing is parsed. The previous form remains valid, of
course. Note that EFL tends to use "scaling" instead of this DPI. The
font DPI is useful for me to open up a terminology window with almost
the same size as my IDE's code viewer.

Use case:

  export EVAS_FONT_DPI=95x94 terminology

Note:
I still don't get a 1:1 match with Qt's rendering, and in fact
94x95 works better than what 95x94 (which is reported by xdpyinfo).
Interesting though :)

@feature