Port TypeScript PR #58816: Use canHaveFlowNode in checkIfExpressionRefinesParameter

[Copilot]

This change ports TypeScript PR #58816 to the Go codebase, which improves flow node access safety in checkIfExpressionRefinesParameter.

Changes Made

Modified checkIfExpressionRefinesParameter in internal/checker/checker.go to use canHaveFlowNode before accessing flow nodes:

Before:

antecedent := getFlowNodeOfNode(expr)

After:

var antecedent *ast.FlowNode
if canHaveFlowNode(expr) {
    antecedent = getFlowNodeOfNode(expr)
}

Rationale

This change mirrors the TypeScript fix that replaced direct flow node access (expr.flowNode) with a safer pattern that first checks if the expression can have a flow node (canHaveFlowNode(expr) && expr.flowNode).

The Go equivalent makes the code more robust by:

• Explicitly checking if a node can have a flow node before attempting to access it
• Following the same defensive programming pattern as the upstream TypeScript change
• Maintaining the same behavior while being more explicit about intent

Testing

• All existing tests pass
• Build completes successfully
• No baseline changes required

Fixes #1129.

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