Add glmnet tests on usage of data descriptors

[hfrick]

These tests are part of addressing tidymodels/parsnip#878

Context: I think we can remove parsnip::eval_args(). It uses parsnip:::maybe_eval() which has a comment that the reason for its existence is related to parsnip's data descriptors.

The goal of this PR is to

• have tests that cover the use of descriptors with glmnet engines,
• show that they pass, and
• then show that they still pass after we remove usage of eval_args() in parsnip and extensions.

@topepo Is there any other usage of the descriptors you had in mind?