Prevent internal class names from being removed

[harshdoesdev]

What's the Issue?

The issue is that when using the classes header to set custom CSS class names, the class names of the kernel elements are being removed.

How to Replicate

fastn code:

-- ftd.column:
css: styles.css
classes: red

-- ftd.text: Hello World

-- end: ftd.column

Expected Output:

<div class="ft_column red"><div>Hello World</div></div>

Actual Output:

<div class="red"><div>Hello World</div></div>

Proposed Solution

In fastn-js/js/dom.js, we can create a map of class names called fastn_dom.InternalClass that will be used by kernel components. Then, in the fastn_utils.removeNonFastnClasses function, we can check if the className that is going to be removed is not one of those class names.