C++: Add support for getting literals in using declarations

[IdrissRio]

No description provided.

[Copilot]

Pull Request Overview

Adds the ability to retrieve the specific member referenced by a using declaration in a templated base class and updates toString() to fall back to this new API.

• Introduces getReferencedMember() in UsingDeclarationEntry.
• Modifies toString() to use getDeclaration() first or getReferencedMember() as a fallback.
• Documents the feature in a new change-notes entry.

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
cpp/ql/lib/semmle/code/cpp/Namespace.qll	Added getReferencedMember() and updated toString()
cpp/ql/lib/change-notes/2025-05-28-using-template.md	Added feature note for getReferencedMember

Comments suppressed due to low confidence (2)

cpp/ql/lib/semmle/code/cpp/Namespace.qll:191

• The use of or between two assignment statements here is invalid syntax and won't produce the intended fallback behavior. Consider computing both descriptions first or use a conditional expression to assign a single result value.

result = "using " + this.getDeclaration().getDescription() or

cpp/ql/lib/semmle/code/cpp/Namespace.qll:192

• getReferencedMember() returns an Element, not a string. You need to call its .getDescription() (or equivalent) to produce a textual representation.

result = "using " + this.getReferencedMember()