compiler: add different scalar types

[gavin-ts]

https://github.com/terrastruct/d2/blob/7f7977eb8b2f7594e72391f2f068715160835536/d2graph/d2graph.go#L45

If it is already valid, I wonder if we shouldn't have it properly set in d2graph.Scalar to use the parsed value instead of Value as a string everywhere and requiring to cast it every time we need to use it

Originally posted by @ejulio-ts in https://github.com/terrastruct/d2/pull/250#discussion_r1036327979