Consume new async light bulb APIs. This makes the light bulb preview pane render asynchronously so that expensive previews don't block the UI thread.

Upgrades System.Collections.Immutable to 1.1.34-rc and
System.Reflection.Metadata to 1.0.19-rc.

TryCombine should never throw exception.

Ensure that speculation analyzer catches replacements which introduces an error type in any of the ancestor expressions.

Fixes internal bug 1086771

First is cleanup some infobar code such as adding copyright header, adding internal, removing unused usings and etc.
Second is adding more info in exception log.
Last is making code action more resilient to null return value from user code.

The API Environment.CurrentDirectory is not available on CoreFX.
Switching all uses to Directory.GetCurrentDirectory which is an
equivalent API (it is actually how Environment.CurrentDirectory is often
implemented).

closes #1829

This changes the compiler APIs to no longer use
RuntimeVersion.GetRuntimeDirectory to find the path to mscorlib and
System.dll for the following reasons:

- This API is not available in CoreFx and hence blocks our transition.
- This behavior of implicitly referencing mscorlib doesn't have a
logical equivalent in coreclr where there may be no reachable mscorlib
on the machine (think Linux).

The compiler now takes the SDK search directory as a paramater.  The
consmer will be responsible for feeding down the correct value to the
compiler.

This is the first step in resolving issue #1939

closes #1943

Handle ConditionalAccessExpressionSyntax expressions within speculation analyzer to ensure that semantics of the conditional access expression and the WhenNotNull part don't change on cast simplication.

Fixes #253

This ensures that code fixes such as Implement Interface Through Member never generate casts that user has to simplify in a subsequent manual step.

Fixes #472

Also add simplifier annotation to using directives / imports statements generated by the code generation service.

Fix spelling mistake.  Add a 'none' kind to HighlightKind to indicate you want the default highlighting for the span.

In particular, it is allowed for arguments to have embedded quoted portions like

/define:Unquoted"Quoted"Unquoted"Quoted"

wich means

/define:UnquotedQuotedUnquotedQuoted

when passed on command line, and should mean exactly the same when passed in an rsp file.

The change fixes #1784

In script and error scenarios, VB and C# syntax nodes corresponding to
constructors/methods/properties/etc. won't necessarily have a parent.
Adding some null checks to prevent a future NRE.

Fixes #317 : This HandleSolutionProjectTypeSolutionFolder was failing
because the msbuild bits in Jenkins were older bits. Now the bits should
have been updated. Hence enabling the test.

In an error parsing scenario, a VB ConstructorBlockSyntax might be
parented by something other than a TypeBlockSyntax.  Added a check for
this scenario.

Fix for issue #786

Do not directly cast symbol to IMethodSymbol

When the user right-clicks on a rule set file in Solution Explorer and
chooses "Set as Active Rule Set", we ask the associated `IVsHierarchy`
for the name of the rule set file and use that to set the
`<CodeAnalysisRuleSet>` property in the project file. However, the name
returned by the `IVsHierarchy` does not include the full path, so this
only works if the rule set is immediately next to the project file.

For linked files this will generally not be the case. Instead, we need
to ask for the *canonical* name, which will give us the full path. We
then compute the relative path to that file from the project's
directory, and use that for the `<CodeAnalysisRuleSet>` property.

Fixes #1579.

Nameof now allows member access from locals, etc. Completion shouldn't
restrict member access to only types and namespaces.

Or, in VB, date literals

Fixing Mef composition error caused by previous commit
(11a827c4)

propagating typo fix

fixing typo

Fixing Mef composition error caused by previous commit
(11a827c4)

Fix CodeFixService.GetProjectDiagnostics to handle compilation end diagnostics. Currently it was just force computing all document diagnostics, not the project diagnostics, which executes the compilation end actions.
Additionally, also fix the BatchFixAllProvider to correctly handle compilation end diagnostics.

    - Adding code refactoring tests
    - Using the error logger for cases where there is not UI to show the user
    - Made sure the cookie registered with the IDE gets unregistered on close
    - Responding to general fixup comments

Updating the extension manager to report code-fix exceptions to the user. In Visual Studio this will cause an infobar to appear giving the user the option to either re-enable the crashing code-fix or re-enable it and ignore future crashes for that session of Visual Studio.

Fixes #1604.
Closes #1605.