Add 'findType', like 'LibraryElement.getType' but...

[matanlurey]

... includes walking export directives.

Open for alternative names, or closing this bug if there is something I'm missing.

[natebosch]

I like findType(LibraryElement, String) as a utility method in this package.

We could consider adding it to Resolver directly - but I like the idea of keeping that class narrow and building up utils here.

[matanlurey]

Me too. Based on my new definition of source_gen, I'd rather keep build to be super-small and stable long-term, while new techniques and utilities go here instead. I'll send a PR.