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

Handle completion items with leading/trailing decorative text

When generating a pinning temp for fixed statements on
fixed buffers, the type for the pinning temp is ref to
the type of the fixed field. However, in our lowering
the type of a fixed buffer field is a pointer type, while
what we actually want for the pinning temp is a ref to
the underlying type. This change fixes that scenario.

Fixes #26335

This change also ensures the projection buffers created in Visual Studio have
the ITextBufferCloneService added to their property bag.

Fixes https://devdiv.visualstudio.com/DevDiv/_workitems/edit/604150

Add VBCSCompiler to SourceBuild.sln

Make the project participate in package restore.

Removal tracked by https://github.com/dotnet/roslyn/issues/26346.

Fix cases where tests fail to clean up files placed in the Temp folder

Removal tracked by https://github.com/dotnet/roslyn/issues/26209.

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

Defer loading of SQLite binaries until they will be used

De-duplicate strings in DiagnosticIncrementalAnalyzer.StateSet