Refactors Publicize connection URL detection

[frosty]

Following on from #17803, this PR refactors the code used to detect success or failure based on the authorization URL. In particular:

• The code has now moved from the sharing web view controller to its own PublicizeConnectionURLMatcher
• I've added unit tests for the URL matching and associated authorize actions
• Most of the matches are now done based on URLQueryItems rather than just looking for substrings of the URL.

To test

• Build and run tests and check they all pass
• Build and run and test out adding as many different accounts in My Site > Sharing as you can. I was able to test Tumblr, Twitter, and Facebook, but I don't have a LinkedIn account to test with.

Regression Notes

1. Potential unintended areas of impact

The ability to connect any of the social accounts that are part of Publicize.

2. What I did to test those areas of impact (or what existing automated tests I relied on)

I added unit tests for the existing URL matching before I made any changes to that code, to verify that my changes didn't have any negative affect there.

3. What automated tests I added (or what prevented me from doing so)

See above. I also added extra tests around the authorize actions too. I added these at the end once I'd moved the authorize action code out of the view controller, as the VC had a bunch of dependencies making it a bit more awkward to test.

PR submission checklist:

• I have completed the Regression Notes.
• I have considered adding unit tests for my changes.
• I have considered adding accessibility improvements for my changes.
• I have considered if this change warrants user-facing release notes and have added them to RELEASE-NOTES.txt if necessary.

[peril-wordpress-mobile]

You can trigger an installable build for these changes by visiting CircleCI here.

[peril-wordpress-mobile]

You can trigger optional UI/connected tests for these changes by visiting CircleCI here.

[guarani]

Hey @frosty, the changes look great! I check for regressions by connecting each of the four (Facebook, LinkedIn, Tumblr, and Twitter) and all connected as expected.
I left some code comments, but no blockers, so feel free to merge as-is.

[jkmassel]

You can test the Jetpack changes on this Pull Request by downloading it from AppCenter here with build number: pr17816-0b54622. IPA is available here. If you need access to this, you can ask a maintainer to add you.

[jkmassel]

You can test the WordPress changes on this Pull Request by downloading it from AppCenter here with build number: pr17816-0b54622. IPA is available here. If you need access to this, you can ask a maintainer to add you.