[ILVerify]Add '--tokens' switch

Today when ILVerify found issue we report tokens/offsets value for type system item for IL methods i.e.

[IL]: Error: [C:\git\corert\bin\Windows_NT.x64.Debug\ILVerification.Tests\Tests\BranchingTests.dll : BranchingTestsType::Branching.FromTryIntoFinally_Invalid_BranchOutOfTry.BranchIntoHandler()][offset 0x00000004] Branch out of try block.

We added some new type check and we decided to not report token value for it because they are not useful for regular use i.e.

[MD]: Error: Interface implementation has a duplicate. Class '[InterfaceImplementation]InterfaceImplHasDuplicate_InvalidType_InterfaceImplHasDuplicate' Interface: '[InterfaceDefinition]Interface'

However there are some scenario where tokens are useful, for instance on obfuscated code. We should refactor code to have token values only if a user pass '--tokens' switch to command line. Reference https://github.com/dotnet/corert/pull/6687#discussion_r241916514

Task list:

• Add --tokens option to command line https://github.com/dotnet/corert/pull/6730
• Include metadata tokens in error messages for new type verifier https://github.com/dotnet/corert/blob/master/src/ILVerification/src/TypeVerifier.cs#L112
• Move IL verifier error message from driver to IL importer and include metadata token only if --tokens is passed

Extra: cleanup code https://github.com/dotnet/corert/pull/6758#discussion_r248405930