Added DataLoader source generator snapshot tests

[glen-84]

Summary of the changes (Less than 80 chars)

• Added DataLoader source generator snapshot tests.

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ℹ️ Notes:

1. I added the package Basic.Reference.Assemblies, as an alternative to loading all assemblies in the AppDomain (like this). I'm not sure which is the better option.
2. I've just added a few tests to demonstrate the snapshotting. Feel free to add more.
3. The snapshots don't look great, because I need to be able to specify the Markdown language per segment (to be discussed tomorrow).

❓ Questions:

1. ✅ All 3 snapshots show a CacheDataLoader being generated – am I doing something wrong? Is the DataLoader type not based on the method signature?
2. ✅ The cancellation token is accessed via _services.GetRequiredService – should it be using the ct parameter of LoadSingleAsync instead?
3. ✅ The generated class name in HotChocolateMiddleware.735550c.g.cs has a variable GUID suffix – is that important? For now, I've added code to replace it with HASH in the snapshots.
4. ✅ I've put the tests in the HotChocolate.Types.Analyzers.Tests project – can the HotChocolate.Types.Analyzers.DataLoader.Tests project be deleted?

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 75.81%. Comparing base (b91ddb7) to head (620ba7c).
Report is 5 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #7290      +/-   ##
==========================================
- Coverage   78.84%   75.81%   -3.04%     
==========================================
  Files        2421     2785     +364     
  Lines      118431   138544   +20113     
==========================================
+ Hits        93379   105035   +11656     
- Misses      25052    33509    +8457     

Flag	Coverage Δ
unittests	75.81% <ø> (-3.04%)	⬇️

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