This reverts commit a96d7825.

This reverts commit 92ff3f8d.

This reverts commit b03e8478.

https://github.com/dotnet/roslyn/commit/b03e84783806dc48f240e56188e6473323dc3ba1

The flag name is "IOperation". Register opeartion actions and calling
SemanticModel.GetOperation while the feature is disabled will throw an
InvalidOperationException. Also log a non-fatal-watson when
SemanticModel.GetOperation crashes.

Right now there are two code paths for signing using a keyfile:

1) Full & delay signing implemented using a strong-name provider, which
   calls into the CLR when necessary to do signing.
2) Public signing, which extracts the key directly from the file and
   embeds it manually into the assembly using only portable code.

The tricky part is that (1) also implements a bunch of legacy semantics
on how to resolve the key file from various search paths, since the key
file can also be specified via an attribute.

This behavior is already deprecated, so rather than implement the
complicated file resolution for public sign as well, this PR changes the
command line compilers to always produce an absolute path for the key
file before passing it to CompilationOptions. CreateCompilation now also
has a check to enforce that CryptoKeyFile is an absolute path when
PublicSign is set.

Fixes #8360.

- IUsingStatement.Body was not visited in VisitUsingStatement.
- IConditionalAccessExpression.ConditionalValue was visited before ConditionalInstance.
- Make VisitNoneOperation virtual

And partially fixed crash in BoundUserDefinedBinaryOperator.get_IBinaryOperatorExpression_BinaryOperationKind()

Also fixes a crash in `BoundConversion.ConversionKind` in C#.

Also fixes crash in `ArgumentBase.IsInvalid` property when code has error.

Replaced all references of `IReferenceExpression` with `IOperation`.

Since it could be `IInvalidExpression` in case of error.

This time it is caused by BontrolVariable bounf to BoundBadExpression.
Also improved the robustness in the Condition property.

Scripting scenarios set a special flag in the ReferenceManager to enable
additional tie-breaking rules in the presence of conflicting references.
Enable that same flag for the EE, which also routinely encounters
conflicting references.

Fixes internal bug 161294.

Renamed more VB private members that implement interface members using the convention of InterfaceName_MemberName.

In cases where it is sopposed to represent error state.

1. Add `invalid` value to `SimpleUnaryOperationKind`, `UnaryOperandKind`, `UnaryOperationKind`,
   `SimpleBinaryOperationKind`, `BinaryOperandsKind` and `BinaryOperationKind`.
2. Make BinaryOperationKind/UnaryOperationKind property return Invalid kind instead of throwing
   exception when handling code with errors.