Use SwiftSoup to parse Open Graph metadata

[joshuatbrown]

Issues covered

#1165

Description

The SwiftSoup implementation of an Open Graph metadata parser.

How to test

Run unit tests

Notes

This PR depends on the API I defined for Open Graph fetching and parsing, which is in #1503. I think of that PR and branch as the main or base branch here, and I plan to create other PRs just like this one with alternative implementations.

We're going with this approach! I've updated this PR to target main.

An alternative implementation for Open Graph parsing is in #1504. It doesn't work.

[mplorentz]

LGTM. This seems like just what we need! And given that #1504 doesn't work for some sites it doesn't seem like a viable option. The way you set it up seems simple and well-abstracted enough to switch out SwiftSoup for some other HTML parser if it causes us problems.

Looking over SwiftSoup's repository, I don't see any discussion of performance or any benchmarks which feels like a bit of a red flag for a parsing library. But I also don't see a lot of issues where people are complaining about performance. It seems well-maintained, so let's give it a shot.