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.