RDFLIB: add getFileContent in rdfLib package.

[zheyxu]

No description provided.

[cdawei]

It seems we also have another function (similar to getFileContent) that parses a TTL string and returns a map: Map<String, dynamic> parseTTL(String ttlContent)

[gjwgit]

... and more logically named too!

[gjwgit]

The aim here is to remove duplicated code from the package, clean it up, use sensible function names.

Is this now in a PR? once merged can be closed.

[cdawei]

I personally think this is not a good fit for rdflib which represents a turtle document using a graph that is more versatile than using a map (as done by getFileContent()).

If representing triples using a map is a common requirement in solid apps we develop, then perhaps adding and exporting a utility function in solidpod to do it.