Remove iron-icon import from vaadin-icons.html

[web-padawan]

Motivation based on the internal discussion:

When doing lazy asynchronous imports, if you try to use some iconset before it was loaded/defined, it won't update iron-icon after the iconset is ready. We have a special bundle for icons on the website, with the import of iron-icons as the last one. But I cannot add vaadin-icons there for the reason above

We can still keep iron-icon as a dependency for backwards compatibility, and even have a separate file importing it as well, in order to avoid breaking change.

[jouni]

The same should be done for https://github.com/vaadin/vaadin-lumo-styles/blob/master/icons.html#L3, right?

[web-padawan]

Yes, I would prefer us having these aligned.

[Haprog]

I guess we could extract the actual iconset definition from e.g. vaadin-icons.html into a new file (e.g. vaadin-iconset.html or just iconset.html) which could be imported in vaadin-icons.html to keep vaadin-icons.html working as before without breaking changes, but this would make it possible to import just the new iconset file without getting the iron-icon dependency.

If we go with the name iconset.html, that file would contain:

<link rel="import" href="../iron-iconset-svg/iron-iconset-svg.html">
<iron-iconset-svg name="vaadin" size="16">
...
</iron-iconset-svg>

And then vaadin-icons.html would basically just contain:

<link rel="import" href="../iron-icon/iron-icon.html">
<link rel="import" href="iconset.html">

(plus some comments that the file now has)

Any comments @jouni @web-padawan?

And then similar change in vaadin-lumo-styles for the lumo icons.

[samie]