ECMAScript.g4 for CSharp

[Eliyahu Peter Kornfeld]

https://github.com/antlr/grammars-v4/blob/master/ecmascript/CSharp/ECMAScript.g4

I run the Java tool to create the CS files, and tried to use it with Antlr4.Runtime.Standard 4.7.1.1 from NuGet (Visual studio 2017)...

There were two problems when compiling:

1. There is no _input variable, but there are several references to it. I defined it and set it's value in the constructor to the incoming ITokenStream... However it may be the base class's InputStream property, but I'm not sure...

2. The La and Lt are in camel-case in the grammar file, but upper-case in IIntStream and ITokenStream...