Fixes #8018.

Internal APIs are aligned with these public APIs.
VB Symbol Display for ByRef returns is adjusted according to the latest design decision.

This reverts commit a03d8b8e.

Fixes #4163.

In some parts of our codebase, we use "verbatim crefs" where the compiler just passes the cref name out to the XML file and doesn't do any analysis of it. While there are some legitimate uses of these, there were many abuses in our source code. Worst of all, in some cases we had verbatim crefs on public types that referenced types that had since been renamed, or the syntax was wrong, etc. With this change, there's now an analyzer that issues a warning for all uses of them. In the places that are fair uses of them, the warning is suppressed. Going forward, adding suppressions should be considered fine as long as:

1) it's a reference to something in another layer or language
2) it's some framework type that's clearly never going to change ever

Otherwise, a proper, verifiable syntax should be used. Again, this isn't to say that verbatim crefs are universally bad, but just that we've proven we make mistakes with them and some guards should be put in place. (changeset 1360175)

To support EnC well the compiler needs to carefully distinguish between long-lived and short-lived synthesized variables. Long-lived variables may cross sequence points and thus need to be mapped the the corresponding variables in the previous generation when emitting EnC deltas. Short-lived local variables shall never cross sequence points.

This change revisits helpers that create synthesized variables and assigns each synthesized variable a SynthesizedLocalKind. Negative kind values are reserved for short-lived variables, positive values for long-lived variables.

The change removed the option to give a synthesized variable an explicit name. The names of the variables are assigned at code-gen time based on their SynthesizedLocalKind. This is to enforce that the names of long-lived variables follow a naming pattern that allows use to reverse-engineer the SynthesizedLocalKind value from the variable name.

Also renames DebugInformationKind.PDBOnly to DebugInformationKind.PdbOnly to follow .NET naming guidelines.
 (changeset 1293017)

Splits Microsoft.CodeAnalysis, Microsoft.CodeAnalysis.CSharp and Microsoft.CodeAnalysis.VisualBasic into portable and desktop assemblies.

Existing Core\Source, CSharp\Source and VisualBasic\Source directories are renamed to Core\Portable, CSharp\Portable and VisualBasic\Portable.
New sibling Desktop folders are added and non-portable source is moved there.
"System.Runtime" references has to be removed in order for the portable project system magic to automatically add facade references.
 (changeset 1281686)

- Disallow field modifiers and field attributes on primary constructor parameters.
- Adjust scope of primary constructor parameters.
- Allow referencing non-ref/non-out primary constructor parameters in a lambda.
- Report appropriate diagnostics when a primary parameter is shadowed in a nested scope.
 (changeset 1261399)

Remove unnecessary Cast method invocations for ImmutableArray that used the same target type as the current type. (changeset 1256408)

Migrated state of “Primary Constructors” implementation equivalent to https://roslyn.codeplex.com/SourceControl/changeset/af3db25146a74523fbb2cf11ef00ddec6c0c3690. (changeset 1249690)

FI Primary Constructor changes from $/Roslyn/AlekseyT/PrimaryCtor up to changeset #1211530. (changeset 1214762)