Script updates

Do not allow private members to be referred to in cref across assemblies

Do not crash when highlighting alias symbols defined via global imports.

Keep track of “bad” attribute applications to prevent PE generation in their presence.

Fixes #1904

Don't recommend #Const after #Const

Allow directive keyword recommenders to differentiate between the start
and middle of a preprocessor directive.

Fixes #722.

Treat System.Void as the absence of a type.

Fixes #1766.

Extend Linux CI support

Couple of changes to the scripts:

- Factored out installing the PCL libraries to setup-pcl.sh.  Makes it
much easier to install PCL against custom builds of mono
- cibuild.sh accepts an optional `—os` option now. Makes it easier to
customize Jenkins based on the OS target.

In some scenarios, an attribute application can be “bad” due to an error type in referenced compilation, but without any diagnostics reported for the referencing compilation.

Added couple tests for ?. operator for cases missed in optimizations.

Test-only change

The tests arep assing, but codegen is not great.

Use msbuild variables for assembly versions of Immutable and Metadata references

This reverts commit 94b22b7c.

The issue was the "DirectCast(Nothing, CompileResult)" (later removed by
commit 90bb89f0).  When compiling without
optimizations, this returns a structure initialized to its default value.
When compiling with optimizations, this throws NullReferenceException.
I've filed bug #2094 for the inconsistency.

Introduce msbuild variables for versions of Immutable and Metadata nuget packages

Retry with System.Core.dll on ERR_NoSuchMemberOrExtension.

Suppress expansion of void* rows

...because they would have type ```void```, which can't be instantiated.

Avoid a hang in CompileWithRetry...

Don't attempt to retry if we're asked to load the same assembly identity more than once.  Adding the same reference won't help anything, and we will almost certainly never terminate the retry loop.

Add support for "dynamic" in the result provider

This is the first of a sequence of changes.  We associate additional
information with each type that comes from the expression compiler.  For
now, it is the bool[] from the DynamicAttribute on the return type of a
method synthesized by the expression compiler.  (The bool[] is packed into
a byte[] for generality and compactness.)  Then, as we traverse the type
in the type name formatter, we consume the flags to determine which
occurrences of "object" should be replaced by "dynamic".

We don't show "dynamic" everywhere we could (e.g. in base type names in
disambiguators), but I believe we show "dynamic" everywhere the legacy EE
did.

TODO: The expression compiler doesn't call the new API to pass the
appropriate dynamic flags (API pending).

TODO: The expression compiler doesn't consume dynamic flags on
pseudo-locals (API pending).

Remove Win10 check from assembly reference resolution...

Ignore enums in OverrideMethodsOnComparable. fixes #1994 

Change uses of FailFast.Assert to Debug.Assert.

In Windows 8 (and 8.1), runtime winmds may contain assembly refs pointing
to other runtime winmds (for example, types defined in Windows.UI.Xaml
point to Windows.UI).  However, when the EE sees these assembly refs it
must redirect them back to the compile time contract assembly (Windows),
because the Compilation used by the EE only references the contract Assembly,
not the various runtime Assemblies.  Previously, we only did this redirection
for Windows 10.  Non-EE cases should only see the contract assembly at
compile time, so this change will not affect them.

Ignore enums in OverrideMethodsOnComparable analyzer and codefixer.
fixes #1994

Add a test for generated IL for a?.b == c in control-flow context.

Removed a duplicated row for the metadata token TypeRef

Ensure that SemanticModel binds with an IncrementalBinder if result of the binding is added to the cache.

update comment and add unit test for VS workspace diagnostic analyzer provider service

Consume new async light bulb APIs from VS platform. 

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

Ensure that SemanticModel binds with an IncrementalBinder if result of the binding is added to the cache.

Fixes #1504.

Add handling of ArrowExpressionClauseSyntax nodes to LocalBinderFactory.