Adding Glean back to the iOS megazord

[travis79]

This is so we can use it to record metrics in Rust on iOS

[codecov-commenter]

Codecov Report

Base: 41.45% // Head: 41.28% // Decreases project coverage by -0.17% ⚠️

Coverage data is based on head (c7b69c6) compared to base (3e570ba).
Patch coverage: 72.72% of modified lines in pull request are covered.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5009      +/-   ##
==========================================
- Coverage   41.45%   41.28%   -0.18%     
==========================================
  Files         167      168       +1     
  Lines       12620    12628       +8     
==========================================
- Hits         5232     5213      -19     
- Misses       7388     7415      +27     

Impacted Files	Coverage Δ
components/nimbus/build.rs	100.00% <ø> (ø)
components/nimbus/src/dbcache.rs	67.30% <0.00%> (-5.61%)	⬇️
components/nimbus/src/lib.rs	64.07% <40.00%> (-0.30%)	⬇️
components/nimbus/src/enrollment.rs	94.90% <100.00%> (+0.02%)	⬆️
components/nimbus/tests/test_telemetry.rs	100.00% <100.00%> (ø)
...ponents/external/glean/glean-core/build/src/lib.rs	0.00% <0.00%> (-92.00%)	⬇️

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[travis79]

There's one more thing to do for this, and that's add test coverage for the metric collection in Rust, I ran into some issues with that and need to speak with Jan-Erik to see what's going on.

It also seems to fail some checks due to the import! macro in glean_metrics.rs 🤔

[travis79]

Seems I forgot to move the exposure event to Rust completely for iOS... not quite ready yet.

[jhugman]

This is looking lovely. 😻

I have added comments which are mostly filing bugs and questions for my own understanding.

I haven't reviewed anything in xcodeproj files, or .h files, and so we should probably ask one of the iOS teams to look at those and give a r+.

From my point of view, this is brilliant, it's been a long time coming, so thank you.

[tarikeshaq]

Thanks a ton @travis79 🚀 🎉 !! Once we get this through we should have a good story for iOS

I had a couple of blocking thoughts/comments that we might need to work out before we land this:

1. The comment about impact on android and possibly feature gating
2. The uniffi version compatibility comment

The rest are nits and questions. I'll timebox sometime to think about the uniffi comment and see if we can comeup with a good way to move forward!

[tarikeshaq]

@travis79 since this has gotten a little stale, do you know what the priority of this work is now? (i.e do we expect we'll get to it anytime soon?)

I don't object to keeping the PR open until we get to it, just curious what a timeline might look like if we have one?

[travis79]

@tarikeshaq Yes, the priorities on this shifted a bit. This is still desirable to do but I don't have time to get back to it immediately. Ultimately I'd love to be able to solve both iOS and Android when we get back to this. Let's close this in favor of starting fresh without any bitrot to deal with.