Fixes #2549

This reverts commit cdf6029c.

Fixes #2631

Centralized some of our scattered uses of reflection to PortableShim.
While moving I verified all of the APIs are a part of the CoreFX +
Portable plan.

Don't ignore reference properties and documentation provider passed to MetadataReference.CreateFromAssembly

Suppress FxCop CA2001 (AvoidCallingProblematicMethods) errors that are being reported for Roslyn's use of Assembly.LoadFrom().

This is cleanup from DevDiv #1043494.

Adds CS0414 (ErrorCode.WRN_UnreferencedFieldAssg / "The field 'X' is
assigned but its value is never used") to the list of error codes that
are not supported in the CSharpCompilerDiagnosticAnalyzer. This allows
CS0414 warnings produced during the build to persist when their relevant
documents are opened in the IDE, which would otherwise cause the
warnings to disappear when the set of live errors is produced.

This removes the majority of references to the deprecated Desktop
assemblies.  The only remaining ones are in the VSIX projects.  They
must remain until we actually delete the assemblies.

Fixes #2604.

This moves the contents of the CSharp and Visual Basic Desktop
Projects to the Portable counterparts.

closes #2587

VB EnC: when lowering conditional branches produce a pattern that allows the debugger to perform function remapping

Fixes #814

If we've already examined an assembly for its references, don't do it
again.

Now that we have checks in place to ensure that the specified set of
analyzer assemblies are the ones that will actually be used for a given
build, we can remove the `CompilerServerFileWatcher` type entirely. This
type watched for changes to analyzer assemblies on disk, stopped
accepting new build requests when it saw any, and then shut down
vbcscompiler.exe once all the pending builds were complete. The goal was
to avoid using an older-but-already-loaded analyzer assembly when there
was a newer one on disk. The new consistency checks are a more reliable
means of achieving the same ends.

Fixes #2324.
Fixes #2377.
Fixes #2495.

1. Update the `Check` method to use `IEnumberable<...>` instead of
`ImmutableArray<...>` for the input parameters.
2. Make the `referenceWhiteList` parameter optional, and provide a
reasonable default.

This commit updates vbcscompiler.exe to reject builds where the list of
analyzers is incomplete (i.e., some of the analyzers depend on
assemblies that are not present), we're unable to load the analyzers, or
the assemblies on disk do not actually match the ones that are loaded.

If one of these checks fails the build request is rejected, and the
clients have been updated to fall back to running the build in their own
process (that is, csc.exe or vbc.exe).

It is possible in some cases that a build that was rejected by
vbcscompiler.exe will succeed in csc.exe/vbc.exe. Generally this will
occur when an analyzer dependency is not passed via the `/analyzer`
switch but happens to be in a place where the CLR will find and load it
automatically. We want to ensure consistency which is why these builds
are not allowed in vbcscompiler.exe; otherwise we risk a build sometimes
succeeding and sometimes failing depending on which assemblies happen to
have been loaded by other, unrelated builds.

1. Replace `MvidsMatch` with the more general `ReadMvid`.
2. Replace `HasStrongName` with the more general `GetAssemblyIdentity`.
3. Assert that we're being given full paths.

1. Make it clear that the methods of `AssemblyUtilities` may throw. They
do not catch and process exceptions themselves as we expect different
hosts will need to respond in different ways.
2. Use `Debug.Assert(...)` to validate parameters on internal methods
rather than throwing `ArgumentNullExceptions`.

Add a utility method to check for strong-named assemblies.

`AssemblyUtilities.HasStrongName` uses the metadata reader to check if
the assembly at a given path has a strong name or not.

This commit includes the code itself and a couple of unit tests. A later
commit will wire it into the compilers/VS.

Add a utility method to identify which of an given assembly's references
are missing from an input set.

This includes the code itself and unit tests. It will be wired into the
compilers/VS in a later commit.

Add a utility method to check that MVIDs match.

Given a path to an assembly and a loaded `Assembly` object,
`AssemblyUtilities.MvidsMatch` returns true if their MVIDs (Module
Version IDs) match, and false otherwise.

This commit contains the code itself and unit tests; a later commit will
wire this into the compilers/VS.

Add a utility method to find assembly dependencies.

Given a path to an assembly, `AssemblyUtilities.FindAssemblySet`
identifies file in the same directory that could satisfy the assembly's
dependencies.

This commit contains just the code itself and some unit tests. A later
commit will wire it into the compilers/VS.

Fixes #2533.