Prevent rendering fields if should not; use hosted pages instead

[makotom]

Overview

This PR introduces logics to avoid rendering hosted fields under circumstances that it shouldn't be rendered.

Background

With 3.1.0, we introduced these 2 changes:

• Support of checkout blocks
• "Truthy" default descriptions of payment methods

As a result an unexpected behaviour was introduced, with which it attempts to render hosted fields unconditionally, even though inline fields are disabled or the publishable key is unset.

It's also worth to mention that there's a non-intuitive design in the WC side for checkout shortcodes. Blocks just need an extra logic to control the behaviour.

Changes introduced

This PR makes these two specific changes:

• For shortcodes: Avoid using default descriptions if other parameters except descriptions indicate that inline fields shouldn't be rendered. This will allow merchants to control rendering of fields by giving blank descriptions. This change also emulates the behaviour in 3.0.9.
• For blocks: Implement an apparatus to tell frontend scripts if it should render fields; the front end script is also revised to honour the passed parameter.

[Dinwy]

Great! Now inline payment is unchecked it is not showing anymore.
Based on this PR, I will fix my #117