Do not replace another `added_to_cart` vanilla handler if there is one

Changes proposed in this Pull Request:

Do not replace another added_to_cart vanilla handler if there is one.

Or jQuery event to Vanilla listener hack for added_to_cart may remove any previous listeners if there are any.

For other events: onupdated_wc_div and onremoved_from_cart we prevent that.

Checks:

[x] Does your code follow the WordPress coding standards?
[x] Have you written new tests for your changes, as applicable?
[x] Have you successfully run tests with your changes locally?
[x] Have you checked to ensure there aren't other open Pull Requests for the same update/change?

Screenshots:

Detailed test instructions:

Simulate another extension listening to the event

add_action(
'wp_head',
function () {
    wp_add_inline_script(
        'woocommerce-google-analytics-integration',
        'document.body.onadded_to_cart = () => { console.log("Other extension listens to added to cart"); };',
        'before',
    );
},
);

Go to shop page
Click add to cart
You should see the console log, and event should be tracked in https://tagassistant.google.com/

Additional details:

Changelog entry

Tweak - Do not replace other extensions' add_to_cart listeners.

woocommerce / woocommerce-google-analytics-integration