Actions: migrate to shared CFG library

Replace the legacy Actions CFG implementation with the shared CFG pipeline, keep data-flow nodes canonical, and ensure callable roots are connected without scalar-expression cycles.

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

Author: owen-mc

actions/ql/consistency-queries/CfgConsistency.ql

@@ -0,0 +1,2 @@
+import codeql.actions.Cfg
+import ControlFlow::Consistency

actions/ql/consistency-queries/qlpack.yml

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+name: codeql/actions-consistency-queries
+groups: [actions, test, consistency-queries]
+dependencies:
+  codeql/actions-all: ${workspace}
+warnOnImplicitThis: true

actions/ql/lib/change-notes/2026-09-29-shared-cfg.md

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+---
+category: breaking
+---
+* The GitHub Actions control flow graph (CFG) now uses the shared CFG library. The CFG includes explicit before and after nodes and uses the shared entry and exit node representations. Existing code that relies on specific CFG nodes, edges, textual representations, or basic block boundaries may need to be updated. The legacy `Completion`, `NormalCompletion`, `SimpleCompletion`, `BooleanCompletion`, and `ReturnCompletion` classes have been removed because completions are no longer part of the Actions CFG API. Code that inspected completions should inspect CFG edge labels such as `DirectSuccessor`, `BooleanSuccessor`, and `ReturnSuccessor` instead.

actions/ql/lib/codeql/actions/Cfg.qll

@@ -1,6 +1,3 @@
 /** Provides classes representing the control flow graph. */
 
-private import codeql.actions.controlflow.internal.Cfg as CfgInternal
-import CfgInternal::Completion
-import CfgInternal::CfgScope
-import CfgInternal::CfgImpl
+import codeql.actions.controlflow.internal.Cfg::CfgImpl