Add Dart plugin

[rvolosatovs]

Closes #100

This PR serves as a starting point for adding back Dart support

[strophy]

@rvolosatovs this was an interesting one! I successfully worked around sgerrand/alpine-pkg-glibc#175 (by manually creating a symlink in /lib64) and sgerrand/alpine-pkg-glibc#185 (using --force-overwrite) but then found the package does not include arm64 builds. There are numerous opened issues and forks, but nothing is properly maintained. So I was thinking the best approach would be to set Dart to no arm64 support. There are also strong rants by Alpine devs against using this package, so it would be nice to somehow drop it.

Then I thought it was strange that Dart is the only language that needs to link against dynamic glibc. After reading the dart Docker Hub docs more closely, they actually advertise extremely small images through a distroless approach. The runtime is supplied in the builder image, and intended to be copied into a FROM scratch runtime image. Since we are using Alpine for the output image, copying this layer of vendored glibc dependencies in seems to have no negative effects, and has the positive effect of simplifying our build by removing the difficult alpine-pkg-glibc dependency, while adding Dart support on arm64.

[rvolosatovs]

Awesome work @strophy ! Thanks a lot!