Don't pass a shared_ptr to SyncManager to the sync client

[nirinchev]

What, How & Why?

Prevents a retain cycle on Apple devices where the sync manager would hold a strong reference to sync client which (through a lambda) would hold a strong reference to the sync manager. We're turning the sync manager reference to a weak one.

I'm not sure how to write tests for that and I'm sorry for the whitespace changes in the readme.

Fixes realm/realm-dotnet#2482

☑️ ToDos

• 📝 Changelog update
• 🚦 Tests (or not relevant)

[fealebenpae]

I’m really not a fan of the whitespace changes in the changelog. Isn’t there a way not to reformat the whole file?

[nirinchev]

I'm not a fan of trailing whitespace - happy to add a linter that adds markdown style rules and fails your builds 😛 but fine, I can revert them, although don't see a point in keeping it in.

[jbreams]

Can you commit the whitespace changes under its own commit? I don't have a disapprove of formatting changes to try to make things cleaner, but including a bunch of unrelated changes in a commit that actually effects behavior is not good code hygiene. And please configure your editor not to do this automatically. For the change log, this is merely a little odd. However, it'd be really unfortunate if this were rewriting a bunch of unrelated code to satisfy your editor's whims.

[nirinchev]

All of that is going to get squashed together anyway, so feels a bit pointless, but definitely not a hill I'm willing to die on. I reverted the whitespace changes as that was easiest and the Core team can decide between yourselves whether the trailing whitespace is worth keeping around or not.

[nirinchev]

The failing tests are not related to this PR and will be addressed separately.