feat(payment): PI-5215 [FE][Google Pay] Implement container mode in GooglePayPaymentStrategy

[bc-wpietrzak]

What/Why?

Add container mode support to the Google Pay payment strategy.
When container is provided (instead of walletButton), a Google Pay button is rendered inside the target element, in place of the Place Order button.

Note: this PR only contains changes related to rendering Google Pay button in the SDK; checkout-js part is still in progress. Both recordings in Testing section have experiment PI-5111.google_pay_direct_pay_on_click on, so stores with disabled experiment won't experience strange behaviour between closing of Google Pay modal and order confirmation.

Rollout/Rollback

Revert

Testing

When container value is provided:

Screen.Recording.2026-05-13.at.02.25.25.mov

When container value is not provided (defaults to using current implementation, walletButton):

Screen.Recording.2026-05-13.at.02.30.17.mov

---

Note

Medium Risk
Changes Google Pay checkout entrypoint by supporting a new container-rendered button and direct-pay flow, affecting initialization, click handling, and teardown paths. Risk is moderate due to new UI/DOM integration and error-handling paths that can impact conversion if misconfigured.

Overview
Adds an alternative container mode to GooglePayPaymentStrategy: when container is provided (instead of walletButton), the strategy renders a branded Google Pay button into the target element and uses that button to launch the payment sheet and proceed with the direct-pay checkout flow.

Extends GooglePayPaymentInitializeOptions with container, button styling options (buttonColor, buttonSizeMode, buttonType), and an onInit(renderButton) hook to defer rendering until the container exists. Updates deinitialization and centralizes Google Pay widget error handling (including mapping CANCELED to PaymentMethodCancelledError), with comprehensive new unit coverage for container initialization, click behavior, and cleanup.

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[bc-wpietrzak]

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[bc-wpietrzak]

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[PavlenkoM]

[optional]

Suggested change

	protected _addPaymentButtonToContainer(
	containerId: string,
	buttonColor: GooglePayPaymentInitializeOptions['buttonColor'],
	buttonSizeMode: GooglePayPaymentInitializeOptions['buttonSizeMode'],
	buttonType: GooglePayPaymentInitializeOptions['buttonType'],
	onError: GooglePayPaymentInitializeOptions['onError'],
	): void {
	if (this._paymentButton) {
	return;
	}
	protected _addPaymentButtonToContainer(
	googlePayOptions: GooglePayPaymentInitializeOptions,
	): void {
	if (this._paymentButton) {
	return;
	}
	const {
	walletButton,
	loadingContainerId,
	container,
	buttonColor,
	buttonSizeMode,
	buttonType,
	onInit,
	...callbacks
	} = googlePayOptions;