Adopt ArgumentParser for the command-line tool

[natecook1000]

This adopts the new ArgumentParser library for parsing command-line arguments.

[benlangmuir]

Hey @natecook1000 this looks really nice. My preference would be to wait until SwiftPM adopts ArgumentParser, then adopt it in sourcekit-lsp and indexstore-db. Until we're using it across the board in sourcekit-lsp+swiftpm, introducing a new dependency creates integration headaches for us that outweigh the benefits in this case (since this is only a tiny test executable).

I'd be happy to keep this PR open until we're ready to take it. Thanks again for the PR

[natecook1000]

@benlangmuir Sounds like a good plan! I'll ping back when we've landed the SwiftPM change.

[shahmishal]

The Swift project moved the default branch to main and deleted master branch, so GitHub automatically closed the PR. Please re-create the pull request with main branch.

More detail about the branch update - https://forums.swift.org/t/updating-branch-names/40412