Merge dev15.1.x to master

Disabling failing ChangeSig test

Factor Windows PDB CDI encoding to a separate shareable type

Flush console out before reading it

Don't offer ?. if it's going to be used in an Expression-Tree.

See https://github.com/dotnet/roslyn/issues/17640

Move to immutable arrays in tests.

Properly compute scope for loops with Inline-Decl.

Disabling the BasicFindReferences.FindReferencesToSharedField and .FindReferencesToLocals integration test.

Moving the Jenkins image to VS2017 RTW.

Preliminary support for the 'Add Parameter' feature.

better file path comparisons

Support multi-dimensional arrays of rank 1 for System.Type arguments of attributes.

Porting VB Classification Tests

* Add missing facades to devdiv toolset

Fixes http://ddweb/buildstatus/issues/issues.aspx?iid=819217

Fixes #4958.

This extends the behavior to constructors, destructors, and operators.
Fixes #17257

Make Fix-All use normal text-diffing as the TreeDiffer produces some very bad results.