Option to compile vendored source from either Samsung or Telegram

[msrd0]

By default, rlottie-sys will keep searching for system-installed rlottie via pkg-config. If not found, it will download samsung's source and compile. Disabling vendor-samsung disables it, enabling vendor-telegram instead downloads telegram's source instead.

I took some inspiration from #56 but chose not to use the cmake crate since I didn't see any value in a poorly documented opinionated glorified wrapper around a binary. If all it did was search for cmake in different install locations and give me a nice api for specifying arguments that would be cool. But unfortunately it sets a bunch of crap without telling you and with no way of opting out. If they fix that and/or someone demonstrates how some obscure operating systems like Windows need that I'd be willing to revisit this decision.

I also added include paths similar to #57 which is now necessary since the vendored source won't be in a default search path.

[github-actions]

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