Merge dev15.7.x to dev15.7.x-vs-deps

Revert "fix for CLR_EXCEPTION_System.NullReferenceException_80004003_Microsoft.VisualStudio.InteractiveWindow.dll (#26770)" (#26892)

This reverts commit db46bcf5.

Merge dev15.7.x to dev15.7.x-vs-deps

See #26339 for the primary RCA.

This change corrects an additional edge case for ITextBuffer instances created before VisualStudioWorkspace attaches event handlers to ITextBufferFactoryService and IProjectionBufferFactoryService. This case is only believed to occur in IDE initialization scenarios where the workspace load is triggered by opening a document.

fix for CLR_EXCEPTION_System.NullReferenceException_80004003_Microsoft.VisualStudio.InteractiveWindow.dll (#26770)

Merge dev15.7.x to dev15.7.x-vs-deps

Move Unshipped public APIs to Shipped

Merge dev15.7.x to dev15.7.x-vs-deps

Desktop signing uses a COM call into the CLR to sign an assembly,
which is not available on Mono or CoreCLR. This change always
uses portable signing by default on Mono as well as CoreCLR.

Merge dev15.7.x to dev15.7.x-vs-deps

Bump version to 2.8.1

Merge dev15.7.x to dev15.7.x-vs-deps

Migrate VSTS YAML to dev15.7.x

update nuget package moniker to `beta6`

disable flaky test

Merge dev15.7.x to dev15.7.x-vs-deps

This copies our VSTS YAML file into dev15.7.x. This changes nothing
about our official build in this branch. It just seeds it with the
correct value and lets the merge bots move it to the rest of the trees.

The official switch over for 15.7 will happen at a later time and will
be very deliberate.

Avoid adding duplicate metadata references to AbstractProject reference list

Fix publish error

Merge dev15.7.x to dev15.7.x-vs-deps

LOC CHECKIN | dotnet/roslyn dev15.7.x-vs-deps | 20180426

skip GenerateMethodInClosedFile test that is already skipped in master

Merge dev15.7.x into dev15.7.x-vs-deps

Revert "Update Roslyn snapshot when editorconfig is updated

This reverts commit f56d67a6.
We are seeing deadlocks where our code tries to fetch the options
for a file, and that code runs on the background thread. The background
thread is trying to hop back to the foreground thread to apply file
watchers for .editorconfig files.

Merge dev15.7.x into dev15.7.x-vs-deps

Fix bad codegen for fixed buffer access

Remove boundnode replacement in lowering in favor of relaxing emit asserts to allow pointer to managed ref assignment for fixed-size buffers

Merge dev15.7.x to dev15.7.x-vs-deps

Use ITextBufferCloneService if available in AsText