Splitting method in two lines between return type and name breaks syntax highlighting #2537

Reproduce the snippet in VS Code 1.27.1 with C# Extension 1.16.1, then locate the repository's C# syntax grammar entry point; no file or test is named in the issue. Done means the split return-type and method-name examples highlight the return type, method name, and method body as they do when kept on one line, including the tuple case.

Environment data

dotnet --info output:

.NET Core SDK (reflecting any global.json):
 Version:   2.1.401
 Commit:    91b1c13032

Runtime Environment:
 OS Name:     fedora
 OS Version:  28
 OS Platform: Linux
 RID:         fedora.28-x64
 Base Path:   /usr/share/dotnet/sdk/2.1.401/

Host (useful for support):
  Version: 2.1.3
  Commit:  124038c13e

.NET Core SDKs installed:
  2.0.2 [/usr/share/dotnet/sdk]
  2.0.3 [/usr/share/dotnet/sdk]
  2.1.401 [/usr/share/dotnet/sdk]

.NET Core runtimes installed:
  Microsoft.AspNetCore.All 2.1.3 [/usr/share/dotnet/shared/Microsoft.AspNetCore.All]
  Microsoft.AspNetCore.App 2.1.3 [/usr/share/dotnet/shared/Microsoft.AspNetCore.App]
  Microsoft.NETCore.App 2.0.0 [/usr/share/dotnet/shared/Microsoft.NETCore.App]
  Microsoft.NETCore.App 2.0.3 [/usr/share/dotnet/shared/Microsoft.NETCore.App]
  Microsoft.NETCore.App 2.1.3 [/usr/share/dotnet/shared/Microsoft.NETCore.App]

To install additional .NET Core runtimes or SDKs:
  https://aka.ms/dotnet-download

VS Code version: 1.27.1
C# Extension version: 1.16.1

Steps to reproduce

1. Open a new .cs file and write the following:

namespace Test
{
    public class TestClass {
        public int
            TestMethod()
        {
            return 2;
        }

        public (int a, IEnumerable<int> b)
            MethodThatReturnsTuple(int x)
        {
            return (5, new [] { 1, 2, 3 });
        }

    }
}

(I know the first example is a bit academic, but I just want to show that even the simpler example fails to some extent. I also note that GitHubs syntax highlight fails the second example... But it is correct csharp syntax)

Expected behavior

Expect highlighting to work as if the methods were on the same line as the return type:

Actual behavior

Note that:

1. In TestMethod, the return type is not correctly highlighted
2. In the MethodThatReturnsTuple, the incorrect highlighting spreads into the method body