Proposal: Add TTF_GetScript to retreive the script to which unicode character belongs

[j9hnny97]

At the moment SDL_ttf provides TTF_SetFontScriptName, a Harfbuzz related function that allows a script to be set (for a specific font) to be used for text shaping.

This is useful as long as the client knows the origin of its texts, allowing him to simply set the script relative to his language. If this isn't the case how would he know what to script to use? And what would happen if there are different characters in his text, each one requiring different scripts?

Harfbuzz already provides a way to obtain the best script to be used by each character. This PR exposes this functionally with TTF_GetScript, allowing the client to deal with this issue however he desires, without compromising the current library implementation.

[j9hnny97]

#312