More Icon Additions for Upcoming Lens Features

[MichaelMarcialis]

Summary

Added some more new icons to EUI to support the needs of upcoming Lens features (thresholds, custom formula). This PR includes the following icons:

• documentation
• layers

Checklist

• Check against all themes for compatibility in both light and dark modes
  - [ ] Checked in mobile
• Checked in Chrome, Safari, Edge, and Firefox
  - [ ] Props have proper autodocs and **[playground toggles](https://github.com/elastic/eui/blob/master/wiki/documentation-guidelines.md#adding-playground-toggles)**
• Added documentation
  - [ ] Checked Code Sandbox works for the any docs examples
• Added or updated jest tests
  - [ ] Checked for breaking changes and labeled appropriately
  - [ ] Checked for accessibility including keyboard-only and screenreader modes
• A changelog entry exists and is marked appropriately

[kibanamachine]

Preview documentation changes for this PR: https://eui.elastic.co/pr_4833/

[cchaos]

I'm curious why not just use the help life preserver icon for documentation? We use it anywhere we direct users to the docs in Kibana.

[MichaelMarcialis]

I'm curious why not just use the help life preserver icon for documentation? We use it anywhere we direct users to the docs in Kibana.

We've received some user feedback in recent Lens testing that the help icon doesn't translate to the idea of opening/reading documentation in their minds. I tend to agree with that feedback, as a life preserver is likely not an object that is immediately familiar to all users. For Lens' case, the plan would be to use this new documentation icon on buttons that trigger the display of more robust "inline" documentation.

[cchaos]

Makes sense. I would make sure to communicate this out to all the rest of the designers and make sure add them to the Figma library.

[kibanamachine]

Preview documentation changes for this PR: https://eui.elastic.co/pr_4833/