chore: fix gulp icons task output
chore: fix gulp icons task output

Now "gulp icons" generates the vaadin-icons.html in the format as we have it now (including comments) so that no manual modifications to vaadin-icons.html are needed and the file can be easily generated after SVG source files for the icons have been updated.

Also added a notice at the top of the generated file that it is generated with this task.

vaadin/vaadin-icons,vaadin/vaadin-icons,vaadin/vaadin-icons