This commit adds support for go/cgo tgs conversion when building with the -tags `cgo`
The default binaries are still "pure" go and uses the old way of converting.
* Move lottie_convert.py conversion code to its own file
* Add optional libtgsconverter
* Update vendor
* Apply suggestions from code review
* Update bridge/helper/libtgsconverter.go
Co-authored-by: Wim <wim@42.be>
