Merge dev15.8-preview2 to master

Merge dev15.7.x to dev15.8-preview2

Extract out a 'relational' section for parenthese preferences

Analyzer Runner tool

Currently AssertIsClosureScopeSyntax is failing for an interpolated string syntax
within particular expression appearing in Analyzer Runner. This change works around
the issue by using simple string concatenation instead.

* Produce errors on emitting attributes using default constructor of structs

* PR Comments

fix for CLR_EXCEPTION_System.NullReferenceException_80004003_Microsoft.VisualStudio.InteractiveWindow.dll (master) (#26910)

Merge dev15.8-preview1 to master

* Update .NET SDK to 2.1.300-rtm-008866

* Set TargetLatestRuntimePatch to false for ILAsm

* Kill build processes after boostrapping phase

* Fix SDK tests

Fixes #16984: Accessors not correctly indented

Add code-styles for controlling parentheses in a project ('coarse' approach).

Improve trivia handling in 'use auto property'.

Even though Roslyn can only every be deployed where at least net461 or netcoreapp2.0 is available Roslyn cannot depend on netstandard2.0 assemblies. This is due to the setup of Visual Studio which has a minimum target of net46 and hence only deploys netstandard1.3 facades. In order to prevent netstandard2.0 versions of NuGet references to deploy, at build or test, we must limit the desktop target framework used in our projects to net46.

There is nothing functionally wrong with having our tests target net461. At the same time though it would mean our tests were running against the netstandard2.0 version of references, such as System.Collections.Immutable, which is not what we deploy against. Hence not testing what we ship which creates a small but real hole.

Add -launch flag to the build script

Reduce async overhead in CodeAnalysis

Example usage: .\build.cmd -release -deployExtensions -launch

fix vsix deployment for integration tests

Fix inline code documentation syntax

Produce much better code for CInt(Fix(number))