Add "Display" versions of the parsed model and the rewritten model in the integration tester

[ozgurakgun]

this made me think: we can also capture the display version of the parsed model and the rewritten model in the integration tester. might make life easier when testing/reviewing prs. a bit redundant if we don't remove the json versions, but json versions contain more info so I wouldn't want to remove those.

Originally posted by @ozgurakgun in #441 (comment)

cc @EEJDempster @Soph1514 is this something for either of you?

[niklasdewally]

Completed by #582