AST: make some classes instance of Scope

ql/src/codeql_ruby/ast/Method.qll

@@ -4,7 +4,7 @@ private import internal.AST
 private import internal.TreeSitter
 
 /** A callable. */
-class Callable extends Expr, TCallable {
+class Callable extends Expr, Scope, TCallable {
   /** Gets the number of parameters of this callable. */
   final int getNumberOfParameters() { result = count(this.getAParameter()) }
 

ql/src/codeql_ruby/ast/Module.qll

@@ -6,7 +6,7 @@ private import internal.TreeSitter
 /**
  * The base class for classes, singleton classes, and modules.
  */
-class ModuleBase extends BodyStmt, TModuleBase {
+class ModuleBase extends BodyStmt, Scope, TModuleBase {
   /** Gets a method defined in this module/class. */
   MethodBase getAMethod() { result = this.getAStmt() }
 

ql/src/codeql_ruby/ast/Scope.qll

@@ -17,6 +17,9 @@ class Scope extends AstNode, TScopeType {
   /** Gets the scope in which this scope is nested, if any. */
   Scope getOuterScope() { toGenerated(result) = range.getOuterScope() }
 
+  /** Gets the scope in which this scope is nested, if any. */
+  AstNode getADescendant() { range = scopeOf(toGenerated(result)) }
+
   /** Gets a variable that is declared in this scope. */
   final Variable getAVariable() { result.getDeclaringScope() = this }