Combine completion script tests

[rauhul]

Removes a ton of redundant completion script tests and combines unique components into a single common set of tests.

[rauhul]

@swift-ci test

[rauhul]

@rgoldberg heads up

[rgoldberg]

@rauhul @natecook1000 Looks like you guys might be getting ready to release a new version.

Any chance of discussing the issue mentioned in the comments of #679?

Thanks for the heads up about this change.

[shahmishal]

@swift-ci test macOS

[rauhul]

@rgoldberg We're happy to take PRs to improve these things, I dont know nearly enough about the completion stuff to have many opinions here

[rauhul]

@rgoldberg My goal is to move all these generators to using ToolInfo instead of the raw internals of argument parser. ToolInfo is basically our easier to use IR for the command structure.

[rgoldberg]

@rauhul thanks for the info.

I've already made many changes in my local branch using the ArgumentParser internals. I know nothing about ToolInfo. Would SAP accept numerous fixes using the internals of ArgumentParser? Maybe I could switch to ToolInfo in a subsequent PR…

Is there anyone else besides @natecook1000 with whom I should discuss #679?

[rauhul]

Lets continue this discussion on #695.

We'd love improvements in this area. Its important for evolution to decouple all these generators from the internals to a more stable API (ToolInfo)