d3d11: Implement d2d/dwrite based text overlay elements
Adding hardware-accelerated text rendering elements and a new GstMeta for text to be rendered at final rener stage.
This patch consists of:
- GstMeta implementation to convey a text rendering information (such as font and formatted text with user defined color), so that the formatted text can be rendred at the final render target suface
- A baseclass for text rendering with timeoverlay implementation
- A custom DirectWrite text render implementation to support various custom features
- Modifying d3d11videosink to support text rendering