Revert "Revert "Disable diagnostic service for projects that we know we don't have all information to provide good results.""

Revert "Disable diagnostic service for projects that we know we don't have all information to provide good results."

Jason left feedback on devdiv side PR about active config change which I didn't thought of before.

so, I tested it and it surfaced some issues. first is, doing reload projects on intellisense build failure can be expensive in some cases, since we already in push mode for workspace events. so, I implemented all the plumbing so that we can just update that one bit.

another issue I found is that, when there is cross language p2p reference A -> B. if B fails on intellisense build, B basically has no information including output path, which means it will not be resolved as cross language p2p reference to A. so, for A's point of view, there is no missing information and think it is fully loaded (since A don't consider B as its dependency), it just thinks one of its file reference (B's output path) is missing. so we end up again shows bunch of errors.

there was no way to resolve this issue except tracking missing metadata reference, so I tried to find cheapest way to track this as much as I can. since we are snapshot model, and file is external to us, I couldnt find a solution which is 100% bullet proof except we checking it every time we create compilation but that is too expensive for the code path. so I check file at the metadata entry point. and rely on our file change notification to correct itself if snapshot become out of sync with reality.

this should fix this another cross language reference issue.

this should make roslyn to turn off full project diagnostics when intellisense build is failed for the project.

when we detect intellisense build failure, VS should put actionable data in error list detail pane.
also bing search for the issue should work as well if one prefer blogs.

this change also fix some issue on cross language p2p references. before there was case where we fail to connect cross language p2p reference causing a lot of errors.

this change also include bulk diagnostic update events improvement. this should let us to deal better (especially when we clean those up) when there are a lot of diagnostics.

moved some more files around diagnostic incremental analyzer and added option to choose between two engines.

     Background:

     As discussed in the dev team all hands all code under the GitHub dotnet foundation is using a single process for contribution, API review, infrastructure and coding style. The idea is to present a unified view to our customer and give them a single story for contributing to any project under the dotnet foundation.

     https://github.com/dotnet/corefx/wiki/Contributing#c-coding-style

     The coding style transition is automated using a Roslyn based rewrite tool:

     https://github.com/dotnet/codeformatter

     This will be applied in stages across our developer tree. Right now the focus is on the Open directory as this is what is being presented on github. Code owners will be contacted before the transition happens.

     Note: this is a soft style requirement. There are no build errors that come from this change.
 (changeset 1408227)