Create consistency with vanilla TS on canEmitSimpleArrowHead

[maschwenk]

I'm doing some regression testing against Typescript Go for emitted javascript, I'm noticing little nuances that are creating differences in emitted output. This is one of those cases.

The logic for canEmitSimpleArrowHead is slightly different where Typescript 5.8 considers whether the parent has modifiers (like async) whereas the Go implementation did not

https://github.com/microsoft/TypeScript/blob/83dc0bb2ed91fe0815ab28dc3ff95fae7425e413/src/compiler/emitter.ts#L4597-L4611

function canEmitSimpleArrowHead(parentNode: FunctionTypeNode | ConstructorTypeNode | ArrowFunction, parameters: NodeArray<ParameterDeclaration>) {
        const parameter = singleOrUndefined(parameters);
        return parameter
            && parameter.pos === parentNode.pos // may not have parsed tokens between parent and parameter
            && isArrowFunction(parentNode) // only arrow functions may have simple arrow head
            && !parentNode.type // arrow function may not have return type annotation
            && !some(parentNode.modifiers) // parent may not have decorators or modifiers
            && !some(parentNode.typeParameters) // parent may not have type parameters
            && !some(parameter.modifiers) // parameter may not have decorators or modifiers
            && !parameter.dotDotDotToken // parameter may not be rest
            && !parameter.questionToken // parameter may not be optional
            && !parameter.type // parameter may not have a type annotation
            && !parameter.initializer // parameter may not have an initializer
            && isIdentifier(parameter.name); // parameter name must be identifier
    }

[Copilot]

Pull Request Overview

This PR updates the logic for canEmitSimpleArrowHead in the printer to align with TypeScript 5.8 behavior by explicitly checking for the presence of modifiers on both the parent and the parameter.

• Introduces explicit nil checks for parent and parameter modifiers
• Reorders validation checks to improve consistency with the vanilla TypeScript implementation

[maschwenk]

Exact output consistency has been communicated as non goal (which makes sense), so closing