Add methods to sanitize shops and hosts

[paulomarg]

WHY are these changes introduced?

When receiving user input data, apps should be able to easily validate that they are in the expected format / safe.

WHAT is this pull request doing?

Adding Utils methods sanitizeShop and sanitizeHost to make it easier for apps to validate / fail requests on a single call.

I ended up opting not to reuse validateShop because I like the ergonomics of

try {
  const shop = Shopify.Utils.sanitizeShop(req.query.shop, true); // Second arg is throwOnInvalid
} catch (e) {
  // Custom error handling
}

// or even no try-catch to just bork since it's a bad request anyway
const shop = Shopify.Utils.sanitizeShop(req.query.shop, true);

better than

const shop = req.query.shop;
if (!Shopify.Utils.validateShop()) {
  throw new Error("this message will be repeated quite a few times");
}

Type of change

• Minor: New feature (non-breaking change which adds functionality)

Checklist

• I have added a changelog entry, prefixed by the type of change noted above
• I have added/updated tests for this change
• I have documented new APIs/updated the documentation for modified APIs (for public APIs)