Add initial support to process CFF fonts contained inside a TrueType font

[BobLd]

This fixes BobLd/PdfPig.Rendering.Skia#46

Prior to this change, we were not parsing the CFF font embedded in a True Type font.

There's only a check for the CFF signature here:
https://github.com/UglyToad/PdfPig/blob/304d7dde5ac70ab07da6989812dbd913ea55298d/src/UglyToad.PdfPig/PdfFonts/Parser/Parts/CidFontFactory.cs#L112C1-L117C26
This only tackle the case where the True Type font is in fact a CFF font.

This PR addresses the case where the CFF font is inside the True Type font. The TrueTypeFontParser already check if the font contains a CFF table, but was not parsing it: The https://github.com/UglyToad/PdfPig/blob/304d7dde5ac70ab07da6989812dbd913ea55298d/src/UglyToad.PdfPig.Fonts/TrueType/Parser/TrueTypeFontParser.cs#L62C13-L62C76

The changes are made to not cause breaking change, but would need a much better test coverage, and potentially some refactoring (e.g. the PdfCidCompactFontFormatFont class cannot be used from TrueTypeFont because it cannot be accessed.