Add ast/tokenizer tests to FSharp.Compiler.ComponentTests

Please add a set of helpers that would allow dumping F# syntax trees and tokens, i.e. results of running the compiler with `--ast` and `--tokenize` flags. That would significantly simplify adding more parser tests, as well as make existing ones cover much more things once they're migrated.

It would be great if the helpers could allow choosing between dumping the tree, dumping the tokens, or dumping both. It could be subsequent `verifyTokens` and `verifyAst` calls.