Fixed NRE in IntroduceVariableCodeRefactoringProvider refactoring

Insert documentation comments in the face of trim_whitespace

scripting hosts: print the submission stack trace only to the console

Merge master to post-dev15.5-contrib

Fix PathMapping to a root directory

The old package had a bug in RunCsc.cmd that didn't properly
quote the dotnet path. When the SDK is upgraded to a sufficient
version by VS, the full dotnet path will be used, which contains
spaces and fails without proper quoting. This updates us to a package
which contains almost the same compilers, but includes the fix for
quoting the dotnet path properly (in PR #23034).

The trim_trailing_whitespace can affect tokens to the right of the caret
so we need to check the token to the left.

Fixed IntelliSense completion for initializing a generic class member when a class member has the same name as generic type argument

Reduce memory allocations in NamingStyle.Capitalize/DecapitalizeFirstLetter

Merge remote-tracking branch 'dotnet/master' into merges/master-to-post-dev15.5-contrib-20171109-080019

* dotnet/master: (33 commits)
  Minor PR feedback.
  Ensure that we track additional member symbols in the VB binder conte… (#23077)
  Address final feedback.
  LCS GetDistance optimization for large differences in sequence lengths (#23081)
  Fix compilation errors after merge.
  Fix typo.
  Small typo fix, add a couple of more tests.
  Fix spelling typos.
  Small refactor.
  Exclude mid statements from compound assignment.
  Add proper In and OutConversion support to C# for ICompoundAssignmentOperation.
  Trivial renames of IOperation API parameter names
  Extract conversion and binary operator logic into reusable components, and refactor all instances to use it.
  Rewrite IPlaceholderOperation to IConditionalAccessInstanceOperation when in that context.
  Fix bug in making GetReceiverOperation static.
  Added test for static With statements and shared fields as RValues.
  Make CreateReceiverOperation return a lazy.
  Fix tests broken after merge.
  Fix the operation verifier code now that getoperationinternal no longer exists.
  Added asserts for static instances.
  ...

Fixed issue with missing suggestion to import namespace if class contains a property with same name as the extension method.

Test for #19609 that looks like have been fixed

Bug fixes for ref readonly

Compound expressions conversions

* Ensure that we track additional member symbols in the VB binder context and populate the additional field/property symbols initialized by VB AsNew clause that initializes more than one field/property

Note: This change also includes an API change to `IPropertyInitializer` as VB WithEvents declaration with AsNew clause initializer can initialize multiple properties.
Fixes #17813

* Fix wording in some comments

* Address review feedback

* Fix build break

Add IgnoredArguments to IVariableDeclarator.

Update static instance handling

Rewrite IPlaceholderOperation to IConditionalAccessInstanceOperation …

Trivial renames of IOperation API parameter names

* dotnet/master: (28 commits)
  Fix the operation verifier code now that getoperationinternal no longer exists.
  Remove usage of IOperation feature flag in newly added unit tests
  More fixes for IOperation tree. (#23028)
  Address PR feedback and remove unused resource and comment out unused error code
  Remove IOperation feature flag and internal registration APIs for operations
  Add unit test for VB
  Address review feedback and add more unit tests
  Fix unit tests
  Fix build errors from merge resolution
  Revert unintentional newline deletion
  Address recent feedback and do not generate an IParenthesizedOperation for C#. This change is now just a test-only change that verifies the current behavior.
  Address PR feedback and use singleton for null instance
  Address PR feedback
  Address PR feedback
  Do not invoke GetStandaloneNode helper in GetOperationWorker
  Fix InvalidCastException in CSharpOperationFactory for invalid nested member initializer (#22983)
  Use ICollection<string>.Contains to avoid Enumerator allocation
  Add IsRef property to IConditionalOperation and ISimpleAssignmentOperation, add RefKind property to ILocalSymbol. (#22933)
  Enable peverify-compat mode for langver < 7.2 (#22772)
  Fix IArgument and IArrayInitializer to have null types
  ...