compiler: Refactor Compiler To Remove Ambiguities

There were significant overlaps in the names of data structures
between the compiler and the language that made it necessary
to litter the code with P4Lang.xxxx. This refactor removes that
requirement in most places (Parser is ambiguous wherever TreeSitter
is used -- cannot avoid that!)

Signed-off-by: Will Hawkins <hawkinsw@obs.cr>

Tests/p4rseTests/CodeGenTests/CodeGen.swift

@@ -41,7 +41,7 @@ func shrink(_ from: String) -> String {
        }
     };
     """
-  let program = try #UseOkResult(Program.Compile(simple_parser_declaration))
+  let program = try #UseOkResult(SpecialCompilers.ProgramCompiler.Compile(simple_parser_declaration))
   let cg = try #UseOkResult(CodeGenerator().codeGen(program))
 
   let expected = shrink(
@@ -73,7 +73,7 @@ func shrink(_ from: String) -> String {
        }
     };
     """
-  let program = try #UseOkResult(Program.Compile(simple_parser_declaration))
+  let program = try #UseOkResult(SpecialCompilers.ProgramCompiler.Compile(simple_parser_declaration))
   let cg = try #UseOkResult(CodeGenerator().codeGen(program))
 
   /// TODO: Fix this test.