Shared: Skip non-CFG children in StandardTree

[hvitved]

Removes the remaining CFG inconsistencies for Rust in DCA.

[Copilot]

Pull Request Overview

This PR updates the StandardTree class in the control flow graph implementation to properly handle CFG children by changing method signatures and calls from AstNode to ControlFlowTree. The changes ensure that only CFG-relevant children are processed, addressing CFG inconsistencies in Rust's Data Control Analysis (DCA).

Key changes:

• Replace AstNode return types with ControlFlowTree in child node methods
• Add deprecated versions of old methods for backward compatibility
• Update all references to use the new CFG-aware child methods

Reviewed Changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 2 comments.

File	Description
shared/controlflow/codeql/controlflow/Cfg.qll	Core changes to StandardTree class, replacing AstNode with ControlFlowTree in child node methods and adding deprecated alternatives
rust/ql/lib/codeql/rust/controlflow/internal/Scope.qll	Updates scope classes to use new CFG-aware child methods
rust/ql/lib/codeql/rust/controlflow/internal/ControlFlowGraphImpl.qll	Updates pattern tree implementation to use new child method
rust/ql/lib/codeql/rust/controlflow/internal/CfgConsistency.qll	Adds file extraction check to deadEnd query predicate

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[Copilot]

The deprecated getFirstChildNode() method returns AstNode but calls getChildTreeRanked(0) which returns ControlFlowTree. This type mismatch will cause compilation errors since ControlFlowTree cannot be implicitly converted to AstNode.

Suggested change

	deprecated final AstNode getFirstChildNode() { result = this.getChildTreeRanked(0) }
	deprecated final AstNode getFirstChildNode() { result = this.getChildNode(0) }

[geoffw0]

I think it can do that conversion just fine. This change doesn't appear to preserve the existing behaviour of getFirstChildNode perfectly, but as it's being deprecated I'm not overly concerned about that.

[Copilot]

The deprecated getLastChildElement() method has the same type mismatch issue - it returns AstNode but assigns from getChildTreeRanked(last) which returns ControlFlowTree. This will cause compilation errors.

Suggested change

	not exists(this.getChildTreeRanked(last + 1))
	result = this.getChildNode(last) and
	not exists(this.getChildNode(last + 1))

[geoffw0]

Code changes and Rust DCA run LGTM.

(I can review the other language DCA runs later if nobody else does it)

[hvitved]

(I can review the other language DCA runs later if nobody else does it)

The other DCA runs are uneventful.