Enable more stages for golden tests

[theunrepentantgeek]

Describe the current behavior

For a number of reasons that were logical at the time, we are currently suppressing/excluding a large number of pipeline stages in NewTestCodeGenerator().

Revisting the list of suppressions in the context of PR #1851, both @matthchr and myself believe that many of these should now be enabled.

Doing so will create a lot of churn in the golden file output from the tests, requiring some close reading to spot anything untoward, so we want to make those changes in a separate PR.

[theunrepentantgeek]

Still required, but should be done at the same time as #2150.

[matthchr]

Some improvements have been made here but there's more to do. Might make sense to do after #2084

[matthchr]

May not actually need to do this -- what we need to do is move off JSON to Swagger

[theunrepentantgeek]

Retaining for now. @theunrepentantgeek to investigate whether we need these.

[theunrepentantgeek]

No longer required; we've decreased the number of suppressions organically and most of the remaining ones make sense.