Fix NRE in WTG1010 when analyzing conditional invoke expressions

[Copilot]

VarAnalyzer.AnalyzeInvoke throws a NullReferenceException when processing conditional access invocations (e.g., obj?.TryGetValue("key", out object val)). The speculative binding of the rewritten InvocationExpressionSyntax fails because a MemberBindingExpression node lacks the conditional access receiver context that Roslyn's binder requires.

Changes

• VarAnalyzer.cs — When the invocation expression is a MemberBindingExpressionSyntax inside a ConditionalAccessExpressionSyntax, rewrite the speculative expression as a regular MemberAccessExpression using the conditional access target so the binder can resolve the receiver.
• VarFixAllProvider.cs — Same fix applied to the ReplaceTypes method which has the identical speculative binding pattern.
• Test data — Added conditional access test case (Lookup?.TryGetValue("key", out string value)) to the Out sample.

if (invoke.Expression is MemberBindingExpressionSyntax memberBinding
    && invoke.Parent is ConditionalAccessExpressionSyntax conditionalAccess)
{
    var memberAccess = SyntaxFactory.MemberAccessExpression(
        SyntaxKind.SimpleMemberAccessExpression,
        conditionalAccess.Expression,
        memberBinding.Name);
    speculativeExpression = proposedInvoke.WithExpression(memberAccess);
    speculativePosition = conditionalAccess.SpanStart;
}