[Milestone] (#1281)

• Add new MS Rules to provide actions & predicates for a number of C#’s
   non-grammar rules:
    - adjacency requirement for tokens in >> & >>=
    - restrict places declaration expressions can be used – as the
      grammar for them is very loose
    - type argument list disambiguation
    - report semantic error if null-forgiving is applied to null-forgiving
    - tweak order of choices in a couple of rules so Antlr picks the right one
• Samples:
   - Reorganise
   - Spilt the large AllInOneNoPreproccesor-v6 into parts
   - Add new samples for new constructs
   - Switch them all to use the new Rules MS

Co-authored-by: Nigel-Ecma <Nigel-Ecma@users.noreply.github.com>

tools/GrammarTesting/Tests/Parsing/ReadMe.md

@@ -7,4 +7,4 @@ The second set, in `Demo`, exist to demonstrate the system and are run when `Set
 or `DoParsingTests` are passed the `-d` option.
 
 If `Demo` is not here it will be in the environment parallel which can be located using the
-environment variable `BG_LIB_PARSINGTESTS`.
+environment variable `BG_LIB_PARSINGTESTS`.

tools/GrammarTesting/Tests/Parsing/Samples/ReadMe.md

@@ -0,0 +1,6 @@
+# Parsing Samples
+
+Sub-directories are used to group related (in some way) tests.
+
+The “v*n*” folders typically contain samples testing features introduced
+in *or before* that version of C# – though nothing is enforced.

tools/GrammarTesting/Tests/Parsing/Samples/v6/AllInOneNoPreprocessor-v6-split/part-A/AllInOneNoPreprocessor-v6-part.cs

@@ -0,0 +1,32 @@
+extern alias Foo;
+
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Linq.Expressions;
+using System.Text;
+using M = System.Math;
+
+using ConsoleApplication2.Test;
+
+/**/
+/* the previous comment is an empty delimited comment and not a document comment */
+/** this is a document comment */
+// this one is a single line comment
+
+using X = int1;
+using Y = ABC.X<int>;
+
+using static System.Math;
+using static System.DayOfWeek;
+using static System.Linq.Enumerable;
+
+[assembly: System.Copyright(@"(C)"" 
+
+2009")]
+[module: System.Copyright("\n\t\u0123(C) \"2009" + "\u0123")]
+
+class TopLevelType : IDisposable
+{
+    void IDisposable.Dispose() { }
+}

tools/GrammarTesting/Tests/Parsing/Samples/v6/AllInOneNoPreprocessor-v6-split/part-A/ReadMe.md

@@ -0,0 +1,5 @@
+# Sample: AllInOneNoPreprocessor-v6-*
+
+This is a standard sample based off a test file originating with the Roslyn project.
+
+The AllInOneNoPreprocessor-v6-* combined contain samples of most of the C# constructs up to C# v6.