compiler: Refactor Transition Statement Compilation

Make it follow the standard protocol(s). Unfortunately that means
that some additional information will have to be carried in
the compilation context. It seems like a decent tradeoff -- but
it may be revisited in the future.

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

Sources/P4Compiler/Parser.swift

@@ -178,8 +178,9 @@ extension ParserState: Compilable {
           sourceLocation: node.toSourceLocation(),
           withError: "Missing transition statement of state declaration")))
 
-    return SpecialCompilers.TransitionStatement.Compile(
-      node: current_node!, forState: state_identifier, withStatements: parsed_s,
-      withContext: SpecialCompilers.Statements.effect(statements: parsed_s, context: context))
+    let updated_context = SpecialCompilers.Statements.effect(statements: parsed_s, context: context)
+      .update(newLexicalContextName: state_identifier).update(newLexicalContextStatements: parsed_s)
+
+    return TransitionStatement.Compile(node: current_node!, withContext: updated_context)
   }
 }