C#: Disallow magic in getAnAccess

[MathiasVP]

Microsoft had a case of bad magic in this predicate when we upgraded to CodeQL version 2.27.0. Here's a partial (awful) pipeline:

[2026-09-17 18:47:43] Evaluated non-recursive predicate m#Variable::Variable.getAnAccess/0#340bbb9f#fb@8b5f56i8 in 441814ms (evaluation was halted due to CancellationException).
Evaluated relational algebra for predicate m#Variable::Variable.getAnAccess/0#340bbb9f#fb@8b5f56i8 with tuple counts:
             7149985     ~3%    {1} r1 = SCAN `Expr::Expr.getEnclosingCallable/0#dispred#f6dee370` OUTPUT In.0
             7149985     ~3%    {1}    | STREAM DEDUP

        269552176500  ~1576%    {2} r2 = JOIN `DataFlowPublic::ExprNode.getExpr/0#dispred#ad3278f4_1#join_rhs` WITH @field CARTESIAN PRODUCT OUTPUT Rhs.0, Lhs.0
                   0     ~0%    {1}    | JOIN WITH Remote::AspNetQueryStringMember#dee4d488 ON FIRST 1 OUTPUT Lhs.1

             7149985     ~3%    {1} r3 = r1 UNION r2
                                return r3

This PR prevents magic in all the overrides of getAnAccess since I wouldn't expect this predicate to ever need magic in any override.

[Copilot]

Copilot review overview

🟢 Approval recommended

The annotations consistently cover the relevant C# access predicate hierarchy without changing query semantics.

Review effort: Balanced
Findings: None

What changed in this PR

Prevents costly magic-set evaluation for C# access predicates.

Changes:

• Adds pragma[nomagic] to base access predicates.
• Applies it consistently to variable, field, property, indexer, and assignable-member overrides.

File	Description
Variable.qll	Disables magic for variable and field accesses.
Property.qll	Disables magic for property and indexer accesses.
Member.qll	Disables magic for member accesses.
Assignable.qll	Disables magic for assignable access predicates.

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