Initial work to add support for external language service result providers for Find All References, GotoDefinition and NavigateTo.

All the newly added result provider interfaces are internal, and would eventually go through API design review to enable third party plugin implementations.

Test/fix scoping rules for pattern locals declared within a local declaration statement

Port fix for an intermittent crash in CompilationWithAnalyzers to future-stabilization

Test/fix scoping rules for pattern locals declared within a using statement.

Fixes #9612.
Related to #8817.

Merge stabilization into future-stabilization

Fixes VSO Bug [199252](https://devdiv.visualstudio.com/DefaultCollection/DevDiv/_workitems?_a=edit&id=199252)

Root cause: We were attempting to access the cancellation token for a cancellation token source within a lambda within the using statement for the token source. If client fires a cancellation before the task within the lambda executes, the token source may have been disposed when the task is eventually activated.

Fix: This change saves the cancellation token for the token source upfront for use within the lambda and also checks for cancellation before computing diagnostics.

Justification for ask mode: We are hitting this intermittent crash in perf runs in an internal VSO branch and fix doesn't have any risks.

Merge remote-tracking branch 'upstream/stabilization' into merge-stabilization-into-future-stabilization20160309-160110

Fixed race in diagnostic tagger

Merge remote-tracking branch 'upstream/stabilization' into merge-stabilization-into-future-stabilization20160309-160110

Merge remote-tracking branch 'vslsnap-roslyn/merge-stabilization-into-future-stabilization20160308-160049' into merge-stabilization-into-future-stabilization20160309-160110

Related to #8817.

https://github.com/dotnet/roslyn/commit/b03e84783806dc48f240e56188e6473323dc3ba1

Port analyzer driver pooling fix to future-stabilization

Non-Fatal Watson if ReiteratedVersionNumber matches when text does not.

Merge stabilization into future-stabilization

change telemetry reporting for rename

Only log formatting events in telemetry when they are enacted by the …

Fix crash if client completes the event queue before the compiler is finished with it.

Allow null Compilation in SymbolDistinguisher.Description.GetHashCode

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

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

Port analyzer allocation fixes from master to stabilization

Fix race condition when generating simulated compilation events

Include HasValue check in BoundSwitchStatement

If the switch expression is a  Nullable<T>  a conditional branch is added for the  HasValue  check.
 That check was added as a separate  BoundStatement  outside of the  BoundSwitchStatement .
 If the lambda rewriter subsequently generated any display class instances, the allocations are added
 as a prologue to the rewritten switch statement but since the conditional branch is outside the switch
 statement, the branch skips the prologue, skipping the allocations. The change is to include the
 conditional branch in the  BoundSwitchStatement  so the branch occurs after the prologue.

[AskMode] Put `IOperation` behind a feature flag

don't assume all reference spans in an inline rename session are projected into the current view

Check file checksums to ensure no corruption occurred.

Include HasValue check in BoundSwitchStatement so any display class allocation is moved outside of the check

Test/fix scoping rules for pattern locals declared within a switch statement.

Test/fix scoping rules for pattern locals

allow cancelation exceptions through the PE stream diagnostic filter

Also fix a bug in lowering of a switch statement where the target expression was not lowered.

Fixes #8815.
Related to #8817.

User scenario: Analysis might get skipped in the IDE for a symbol/partial declarations for a partial symbol with more than one definition in a single document.

Cause: When computing symbols declared in the tree to generate symbol declared events, we were adding duplicate entries if a symbol had more than one partial declaration in a tree. This meant that multiple threads might start performing symbol analysis on the same symbol, causing a race condition as driver doesn't expect duplicate events. Though we ensure not to make duplicate callbacks, we might end up missing on making some callbacks at times.

Fix: Compute only unique symbols from declarations in a tree.

Risk: None, it is a trivial fix.

Testing: Before the fix, I was able to repro the race condition and the assert consistently by running the flaky test in a loop for over 10k times. After the fix, it doesn't repro on running the same multiple times. A new unit test has also been added, though it did not fail consistently even before the fix.

Fixes #9462