Use debug printing for expect_test in the parser and other places.

[sezna]

We currently use ToString::to_string (i.e., Display) in our expect test tests for the parser (see here). This is problematic, because this trait is typically used for user-facing representations of data structures. We are forced to choose between a pretty user-facing representation, and a more technically accurate debug-style representation for testing for namespace names in #1312 as a result.

[Pulkit1822]

@sezna , I would like to work on this issue.