The argument that stands for the receiver of a `ref` extension method must be always passed as `ref`

Snap master into dev15.6.x

Skip pseudo-variables with use-site errors

* Simplify codegen for struct declaration patterns
* Move box to perform the conversion only when the test succeeds

Avoid skewing analysis time when logging analyzer times

Be resilient to the OOP process going away in TodoComments and DesignerAttribute processing

Fix ArgumentException when creating diagnostic with effective severit…

* Reject ref as an invalid modifier for accessors

* Updated test plan

* PR Comments

* Accept ref in parsing, and error out in binding

* Update test plan

* Fix build break

Do not autodisable verification based on unsafe compilation option.

MemberSemanticModel.GetBoundLambdaOrQuery should use GetAdjustedNodePosition helper to ensure proper handling of zero-length tokens at the beginning of a syntax node. (#24049)

Fixes #23883.

Fixes VSO 547049

* added Microsoft.VisualStudio.IntegrationTest.Setup.vsix to signing

* removed duplicated entry.

* now test setup vsix is part of signtooldata.json no need to have special case for it.

also made exception to have better message

Merging on behalf of @alrz. Thanks!

There were two separate bugs here:
    1) Fixing up the MVID of the binary was being done *after* signing,
    when it should be done before.

    2) System.Reflection.Metadata has a bug where calculating the
    checksum occurs before signing, when it should happen after.

Both of these isues have been fixed and the helper utility that checks
to see whether a binary was signed has been changed to verify that the
signature and checksums of the binaries are valid, not just that the
signed bit is set on the assembly.

Fixes #23521

Merge dev15.6-preview2 to master

Merge remote-tracking branch 'dotnet/dev15.6-preview2' into merges/dev15.6-preview2-to-master-20180104-080013

Removing the rename command target from Roslyn as it will be part of core editor platform

Merge dev15.5.x to dev15.6-preview2

LOC CHECKIN | dotnet/roslyn-master | 20180103

Merge dev15.5.x into master

Correct date stamping logic for the new year

Ideally, we'd apply a version number to our binaries like 20180102
for the 2nd of January, 2018, but the Windows PE file format restricts
each number to a 16-bit unsigned integer. This means even trimming
to 80102 still isn't enough. The solution is to continue to decrement
that 'year' digit, and each time we do so add another 12 to the month.
This buys more time until we can rebaseline where we start.

Add MEF metadata to IDeferredQuickInfoContentToFrameworkElementConverter

Merge dev15.6-preview2 to master

LOC CHECKIN | dotnet/roslyn – master | 20171222