Changes include:

1. Enhance CompilationWithAnalyzers to allow computing analyzer diagnostics for a specific tree/span within a compilation and/or for a subset of analyzers. Implementation ensures no duplicate analysis by tracking partial analysis state and caching the reported analyzer diagnostics.

2. Overview of the new APIs added to CompilationWithAnalyzers:
    1. GetAnalyzerSyntaxDiagnostics(tree, analyzers, ct)
        1. Analogous to SyntaxTree.GetDiagnostics(ct)
        2. Gets analyzer diagnostics reported by executing syntax tree actions on the given tree.
    2. GetAnalyzerSemanticDiagnostics(semanticModel, spanOpt, analyzers, ct)
        1. Analogous to SemanticModel.GetDiagnostics(spanOpt, ct)
        2. Gets analyzer diagnostics reported by executing rest of the non-compilation actions on the given tree span.
    3. GetAnalyzerCompilationDiagnostics(analyzers, ct)
        1. Gets rest of the analyzer diagnostics which are reported by either of the following means:
            1. Compilation actions (and compilation end actions)
            2. Non-compilation actions reporting diagnostics on different tree: Executing a symbol action on a symbol definition in a tree, can report diagnostic on its partial definition in some other tree.

3. Simplify IDE analyzer driver by switching it to using the new CompilationWithAnalyzers APIs for analyzer diagnostic computation. Both the IDE and compiler drivers now use the compilation event queue model for driving analysis.

DiagnosticIncrementalAnalyzer.LatestDiagnosticsForSpanGetter.VerifyDiagnostics
checks that the diagnostics returned by the SemanticModel for a given span
are the same as the diagnostics returned by the SemanticModel for the
whole document after filtering down to the span.  This check fails when
the span includes unused import diagnostics, because they are never
reported by the SemanticModel when a (sub)span is given.

"Roslyn" -> "Microsoft" or "Microsoft.CodeAnalysis"

At the moment, these aren't used by any completion providers in the features layer. Until we decide that this is ready to support cross-platform, let's keep them in the editor features layer closer to the providers that actually use them.

- apply feedback: unify C# and VB

It updates earlier C# implementation and ports to VB (#3894)

A large change again, mostly mechanical. There's a fair amount to clean up and that will come in the next commit.

This one is a much larger change but is mostly mechanical.

This change touches a lot of files but most of the changes are
mechanical. Essentially, this introduces a CompletionItemRules type as a
means to customize the behavior of a CompletionItem. This will
ultimately be the home of several methods that currently reside on
CompletionListProvider (such as IsCommitCharacter and
IsFilterCharacter), but only the SendEnterThroughToEditor method has
been moved in this change. Other methods will be moved in future
changes.

Fix #3894. Note that VB porting will be followed.

This is willfuilly inconsistent with the methods in CodeFixProvider, CodeRefactoringProvider
and DiagnosticAnalyzer becuase the name feels a bit better in this case. This might be changed
following an API design review before being made public.

* Convert the ICompletionProvider interface to a CompletionListProvider abstract class.
* Rename CompletionItemGroup to CompletionList
* Introduce a CompletionListContext type to be used by providers to specify the contents and
  details of CompletionLists with a RegisterCompletionListAsync() method.
* Change GetGroupsAsync() method to GetCompletionListAsync(), which returns Task<CompletionList> rather
  than Task<IEnumerable<CompletionList>>.
* Move code that merges, de-dupes and sorts completion lists from the controller into the
  completion service. This affected a few VB spell check unit tests which now change their ordering
  slightly.

This moves all of the InternalsVisibleTo which were defined in code into
the project files where the majority of the IVT definitions lived.

The targets files were previously split into an open version in
Microsoft.CodeAnalysis.Toolset.Open and a closed version in build/. This
unifies the four targets into two new targets, VSL.Settings.targets and
VSL.Imports.targets, and moves all the targets from ..Toolset.Open into
the build/ folder.

This propery was essentially unused. It was only ever checked by the SuggestionModeCompletionProviders
and in that case, it was always true.

Currently, the C# and VB suggestion mode completion providers both implement ICompletionProvider
in nearly the same way. This change introduces a new base class containing the shared
implementations.

Note: prior to this change, C# and VB returned different values for IsCommitCharacter: false and
true respectively. Now they'll both return false. However, this is OK because the completion
controller handles builder completion items specially and IsCommitCharacter so that is never
actually called in this case.

This fixes #3604 by passing the display name for rude edit diagnostics.

This reverts commit 15443a23.

Conflicts:
	src/Compilers/CSharp/Portable/CommandLine/CommandLineParser.cs
	src/Compilers/CSharp/Portable/PublicAPI.txt
	src/Compilers/Core/Portable/PublicAPI.txt
	src/Compilers/VisualBasic/Portable/CommandLine/CommandLineParser.vb

Fixes #2888
Fixes #3786

ProjectId for HostArgId can be null for workspace diagnostic exception. make sure we guard from it.

Fell out of our normal cadence for this during the push for RTM. Now that we
had a bit more breathing room getting us back on track here.