Don't expose the disposed ServiceProvider instance

[ganhammar]

The IServiceProvider instance in the ResolveEventStreamContext has been disposed at the point where it gets exposed to the subscription resolver and any data loaded fields included in the GraphQL request. With this PR it is set to null instead of the disposed instance. See discussion here.

I don't know if you would like to see tests for this change?

[ganhammar]

@Shane32 I think this is the change you suggested?

I don't know if the issue should be moved from the server project and be linked with this PR?

[sungam3r]

Rel: graphql-dotnet/server#706

[Shane32]

@ganhammar yes thanks. It looks like the branch needs to be merged with the current 'master' branch so that we can let it run the tests and merge it.

[ganhammar]

@ganhammar yes thanks. It looks like the branch needs to be merged with the current 'master' branch so that we can let it run the tests and merge it.

Yeah, sorry, I missed that I already had forked the repo a while back, so didn't pull latest changes. Fixed now!

[codecov-commenter]

Codecov Report

Merging #2847 (652fdc2) into master (157074f) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master    #2847   +/-   ##
=======================================
  Coverage   83.78%   83.78%           
=======================================
  Files         364      364           
  Lines       14978    14979    +1     
  Branches     2369     2369           
=======================================
+ Hits        12549    12550    +1     
  Misses       1798     1798           
  Partials      631      631           

Impacted Files	Coverage Δ
...QL.SystemReactive/SubscriptionExecutionStrategy.cs	88.19% <100.00%> (+0.08%)	⬆️

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[Shane32]

@sungam3r look good?