[Backport] Disable add to cart button when redirect to cart enabled

[rogyar]

Original PR: #14060

Description

Disable add to cart button when redirect to cart enabled, it includes product validation.

Pre-requisites

1. Install Magento 2.1.x
2. Go to Admin >> Stores >> Configuration >> Sales >> Checkout
3. In "Shopping Cart" section change "After Adding a Product Redirect to Shopping Cart" to "Yes"

Manual testing scenarios

1. Go to product page on frontend with very slow internet connection (could be emulated in chrome)
2. Click "Add to Cart" button

Expected result

1. After clicking "Add to cart" button should became to disabled
2. Button color should be changed to "disabled" (grey)
3. Text on "add to cart" is changed to "Adding...", then to "Added"

Actual result

1. After clicking "Add to cart" button is not became to disabled
2. Button color is not changed to "disabled" (grey)
3. Text on "add to cart" is not changed to "Adding...", then to "Added"

[magento-engcom-team]

Hi @rogyar. Thank you for your contribution.
Changes from your Pull Request will be available with the upcoming 2.1.15 release.