Python: adapt to new shared CFG signature

Main added two new requirements to AstSig:
- A 'Parameter' class with a 'getDefaultValue()' method, plus a
  'callableGetParameter(Callable, int)' predicate.
- A 'CallableContext' class in InputSig1, replacing the previous
  'CallableBodyPartContext'.

Add stub implementations: 'Parameter' is empty (none()) and
'callableGetParameter' returns nothing, mirroring Java's TODO. Rename
'CallableBodyPartContext = Void' to 'CallableContext = Void' in the
Python Input module.

NewCfg evaluation-order tests still pass at the 22/24 baseline; all
11 shared-CFG consistency queries still report 0 violations on
CPython.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

python/ql/lib/semmle/python/controlflow/internal/AstNodeImpl.qll

@@ -165,6 +165,20 @@ module Ast implements AstSig<Py::Location> {
   /** Gets the body of callable `c`. */
   AstNode callableGetBody(Callable c) { result = TBlockStmt(c.asScope(), "body") }
 
+  /**
+   * A parameter of a callable.
+   *
+   * TODO: Implement in order to include parameters in the CFG.
+   */
+  class Parameter extends AstNode {
+    Parameter() { none() }
+
+    Expr getDefaultValue() { none() }
+  }
+
+  /** Gets the `index`th parameter of callable `c`. */
+  Parameter callableGetParameter(Callable c, int index) { none() }
+
   /** A statement. */
   class Stmt extends AstNode {
     Stmt() { this instanceof TStmt or this instanceof TBlockStmt }
@@ -1119,7 +1133,7 @@ private module Input implements InputSig1, InputSig2 {
     string toString() { result = "label" }
   }
 
-  class CallableBodyPartContext = Void;
+  class CallableContext = Void;
 
   predicate inConditionalContext(Ast::AstNode n, ConditionKind kind) {
     kind.isBoolean() and