Adding a way to extract an unscaled character with metrics.

Also including a check to see whether a character is present in the font.

This is a bit of an ugly hack in its current form, since it essentially duplicates the `getGlyphIndexCurvesAtPointSizeAndPos` function internally. The biggest difference is that the origin falls on the baseline instead of the top of the bounding box, and the exact em scale is also provided, which is necessary for me to create my own font rendering system. Other than that, the old function could be probably easily implemented by using the new `getUnscaledGlyphIndexCurves` directly and transforming the coordinate system.