C#: Move handling of callables into shared control flow library

[hvitved]

In preparation for adding parameters to the CFG, which we also want the shared CFG library to handle.

[Copilot]

Pull request overview

This PR refactors callable-handling in the shared control-flow library to support upcoming CFG parameter support, moving language-specific “multiple body parts” handling behind a shared interface.

Changes:

• Extends the shared CFG AST signature with a CallableBodyPartContext and callableGetBodyPart hook.
• Updates shared callable entry/exit and stepping logic to work with either a single callable body or multiple ordered body parts.
• Adapts Java and C# CFG inputs to provide an appropriate CallableBodyPartContext (Void for Java, CompilationExt for C#) and moves C# constructor/initializer body-part handling into callableGetBodyPart.

Show a summary per file

File	Description
shared/controlflow/codeql/controlflow/ControlFlowGraph.qll	Adds shared callable body-part abstraction and integrates it into shared CFG construction/consistency checks.
java/ql/lib/semmle/code/java/ControlFlowGraph.qll	Wires Java into the new shared callable body-part interface using Void as context.
csharp/ql/lib/semmle/code/csharp/controlflow/ControlFlowGraph.qll	Moves C# constructor/initializer callable handling to callableGetBodyPart and introduces CompilationExt as context.

Copilot's findings

Comments suppressed due to low confidence (3)

shared/controlflow/codeql/controlflow/ControlFlowGraph.qll:470

• Wording in doc comment: "indexth" is awkward; consider using "index-th" (or "indexth" without code formatting) to avoid the grammatical glitch.

     * Gets the `index`th part of the body of `c` in context `ctx`.
     *

shared/controlflow/codeql/controlflow/ControlFlowGraph.qll:472

• Doc comment is a bit ambiguous because callableGetBody is a function: instead of "must never both hold", consider wording like "must never both produce a result" / "must not both be defined" for the same callable c.

     * `callableGetBodyPart(c, _, _)` and `callableGetBody(c)` must never both hold
     * for a given callable `c`.

shared/controlflow/codeql/controlflow/ControlFlowGraph.qll:2183

• The comment "included in both callableGetBody and callableGetBodyPart" is unclear (since these are relations/functions rather than collections). Consider rephrasing to explicitly state that it holds when both callableGetBody(c) has a result and callableGetBodyPart(c, _, _) has a result for the same c.

          /**
           * Holds if `c` is included in both `callableGetBody` and `callableGetBodyPart`.
           */

• Files reviewed: 3/3 changed files
• Comments generated: 1

[aschackmull]

Generally LGTM. I have a few slight preferences for some small tweaks, though.

[hvitved]

DCA reported alert difference for C#, which happens because in some cases the same Compilation can have multiple body parts at the same index. The CFG before would branch out to each part, while not ideal, it is better than skipping body parts, which would happen because the rank indices generated in the shared code were not consecutive. I have added a commit that uses dense ranking throughout in the shared library to prevent such cases.