Remove all preorder walks of interval trees.

Replace Cci.SecurityAction with System.Reflection.DeclarativeSecurityAction

Add two new dev solutions to the root

Right now we have CrossPlatform, Roslyn, and RoslynLight, all of
which are heavyweight except for CrossPlatform, but xplat isn't
a fixed set of projects, just whatever we can build xplat. This change
adds two new solutions for developers to choose, depending on what
they're working on. The Workspaces solution contains everything
workspaces and down, while the compilers solution just contains the C#
and VB compilers.

Adds two new projects, CscCore and VbcCore, which target CoreCLR and
produce CoreCLR-compatible executables in the core-clr subdirectory of
the build output. At the moment they are not included in any solution
because a bug in the DNX build tools that causes VS 2015 to deadlock
whenever the project files are loaded.

Unit test assembly for our MSBuild tasks

Remove CompletionTriggerInfo.IsAugment property

This is the start of our unit test assembly for our MSBuild assets.

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.

Unify C# and VB suggestion mode completion providers

More PE Writer cleanup

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.

Remove special VB Implements/Inherits statement completion list provider

Text section header cleanup

There is a special completion list provider in VB for showing completions within Inherits or Implements
statements. This change removes that customer completion list provider and pushes its logic down into
the recommendation service. That way the Recommender API will correctly return these symbols, and the
symbol completion provider will service them up into the completion list.

Because the Implements/Inherits completion list provider produced an exclusive lists, a small tweak needs
to be made to the built-in type keyword recommender. Otherwise, keywords like 'Boolean' would be recommended
after Inherits, which isn't legal. Additionally, I've added a unit test to verify that 'Global' **does**
show up after Inherits and Implements.

Remove unused PE sections

[Bug][VB] RudeEdit error message blindly blames AutoProperty

It fixes #3605

It fixes #3605

Remove dependency on Microsoft.CodeAnalysis.Workspaces

FixerWithFixAllAnalyzer references types in the Workspaces assembly in a
couple of places:
``` C#
private static string CodeFixProviderMetadataName = typeof(CodeFixProvider).FullName;
```

This creates a runtime dependency on Microsoft.CodeAnalysis.Workspaces.dll
which is part of VS but not part of the compilers (csc/vbc/vbcscompiler).
The analyzers that derive from this type thus work in VS but fail during
build with a `TypeInitializationException`.

The fix is to use hard-coded strings for the names of these types. As
they are part of the public API, their names won't be changing anytime
soon.

This does not remove the project-to-project reference to Workspaces.
Doing so would have required fixing up a bunch of `<see cref="..." />`
elements in the doc comments to use the full name of these types as well,
generally making them much uglier. This isn't necessary to fix the
runtime issue.

Fixes #3706.

FixerWithFixAllAnalyzer references types in the Workspaces assembly in a
couple of places:
``` C#
private static string CodeFixProviderMetadataName = typeof(CodeFixProvider).FullName;
```

This creates a runtime dependency on Microsoft.CodeAnalysis.Workspaces.dll
which is part of VS but not part of the compilers (csc/vbc/vbcscompiler).
The analyzers that derive from this type thus work in VS but fail during
build with a `TypeInitializationException`.

The fix is to use hard-coded strings for the names of these types. As
they are part of the public API, their names won't be changing anytime
soon.

This does not remove the project-to-project reference to Workspaces.
Doing so would have required fixing up a bunch of `<see cref="..." />`
elements in the doc comments to use the full name of these types as well,
generally making them much uglier. This isn't necessary to fix the
runtime issue.

Fix modified path to nuget.exe

RudeEdit error message has a placeholder not filled in

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

Fix typos

Remove reference to Cci.IModule from PEWriter

PEWriter refactoring: sync PE header structures with those of PEReader

More PE header tests