[Activate] During log-in, after entering mismatched WordPress.com email address, improve the error handling.

[hafizrahman]

In the case where merchants enter a mismatched WordPress.com email address, the app opens this LoginNoWPcomAccountFoundFragment screen:

We want to improve various aspects of this flow / screen to help merchants use their site with the app.

Internal ref: pe5sF9-oC-p2

For the first iteration, here's what we want to do:

• [ ] The "Enter Your Store Address" button is shown when merchants start from the "Enter Store Address" flow. This creates a loop and should be removed. #7128
• [ ] Add a "What is WordPress.com" button similar to other places on the login flow. #7147
• [ ] Review the existing error message and improve the wordings if needed.