Update vue-gtag.d.ts

[mwargan]

Adds currency to EcommerceAction see #566 (comment)

No further changes required.

var purchase = (function (params) {
  event("purchase", params);
});

^ looks like it will pass the currency as needed, and from there Google will know what to do with it.

[mwargan]

Note the typing is also used for the "refund" event, which is OK as Google Analytics also accepts, and even requests, a currency - see "* If you set value then currency is required for revenue metrics to be computed accurately.". This is also true for the Purchase event - see https://developers.google.com/analytics/devguides/collection/protocol/ga4/reference/events#purchase

@MatteoGabriele we may need to include a bit more advanced/dynamic typings to enforce this and/or do it on the code level.

[mwargan]

@MatteoGabriele I have updated the types to make currency required if value is present, as per the Google docs. You can play with it here:

https://www.typescriptlang.org/play/?#code/ATD0CpwKBZ2AAgZwKYuACwC5YA5IC5RQATFANxQBsB7XFAJyQDoBzGm1qlZgYxoC2oAIYA7YVQCeWAJa8kpCqwCuMsgv5VuvWTVGhWWYawBWClKIxjeKEgFoU-AQMY2AxMJ0y9AfRLCjGBBwUCCUAA9cGgYsYBlRLEYAM090AFEnFwYbAEEvPQAhYVRgAG8gkAh4AFVRGQBHZXQASQARYCTo4CwMdCwGMSRPXVFmOFDYboHRIfzRHzUCYCR++NYAbgqwSGAAFV7lrGj0LuEkpJkqGQDvUQ6GQWAAdww5DG7XpCnB4dvgGl4vGUDAYtnGWzOFyuNz0AH4lisGGtNpMqnthOFgMIBDRlAlwZMjOF4cBRMoBAAjRgo2BogDKr1wuDWwH4KwJsCQjOZolYJLJlOpWzR+3QwhBwkkrL0RniLJ6YqQSAB10SJGAuAeJGUOi+IS2MkSAiQJIA4kZWMxmkaANoAXRplR2osOKFwwAAFMJSeSqQwAJRxO4K1m9XgAa1xsU1AJQSo5IF4YcjyiwPhWbv5vqFqJ2AGFk1H-rgRp6ZMweMtqI41RrJS58S4ejQSIH9ZMk44U2m6CMSYjkUEAL5BMKRaKxeKJBgpGzADKCLK5OYAdUNGDzwNBol4UoiiVEJC+C+crhQeRGRRK5Vz8AAahImmWK8wADTAUGUMkoQPFZW8VUwSedcPnQCgLFidtYHIR8UCWAU-UdbZ4BdIEQQsXd-iSUDgBgqgnygxMtwwyQEVWXkaRHEAxyiGIg2nWd0kyM8L1uNdm1TTd0J3PdwgPI952Y7JzzmK90BvWkdgffD0A9cseHfT8LCaX8lRVAIgJAkNwPxQjcNgkk8TIC5RFsJCRQONDt0wmhsJDPCCImWArJIwzDxQEyzOHUcQAiWjYiwSR6EExcWLmYAAF4QtPYTWL0diN2InjgAAH2ipcRJGBKoy46zJE2KBuFiYCelykilhPDK4tEAqSsS7jMKiiSQH6H45gWEgCAAIgARi618tgcuCeoGjskt3JYuuqOlWi6qAR0KlBivXHLxtI9KwpGWqVs4tbIrKLZWpmX5fEWXr+sG2CCB6+aCqK54dqwMqeJyQ9pKaCqhOXLaoCgOrVoayRXpId70Caw7plmEYOu6vrbqAA

[mwargan]

I've added a final touch-up to enforce that the currency is exactly 3 letters and uppercase

[mwargan]

@MatteoGabriele can we get a move on this? This is actually quite important because this param is required according to Google.