ast.TestCheckErrors is getting out of hand

[eaburns]

First, all of the []string{...} boilerplate should probably go away. The few tests that need multiple packages can be done separately, not in the table.

Second, this test is huge. The table is segmented with comments. Instead, the test framework should be factored out, and the test should be broken into multiple separate tests based on the current table segmentation. This would allow them to be run in parallel in some future world where we actually call t.Parallel()