Adding prepend and append to EuiSuperSelect

[elizabetdev]

Summary

This PR adds a prepend and append to EuiSuperSelect. And it's required to finish the EuiColorPalettePicker.

It can be tested in the Super Select States section of the docs.

Checklist

• Check against all themes for compatibility in both light and dark modes
• [ ] Checked in mobile
• Checked in IE11 and Firefox
• Props have proper autodocs
• Added documentation 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_3167/

[chandlerprall]

Code changes LGTM! Docs work as expected

[cchaos]

Hmm, it looks like adding that overflow:hidden also hide the shadow:

Before

After

[kibanamachine]

Preview documentation changes for this PR: https://eui.elastic.co/pr_3167/

[kibanamachine]

Preview documentation changes for this PR: https://eui.elastic.co/pr_3167/

[elizabetdev]

Hi @cchaos,

I tried a different approach. Now I'm adding the overflow: hidden to the .euiFormControlLayout__childrenWrapper only when the prepend/append is true.

I also added a test.

[kibanamachine]

Preview documentation changes for this PR: https://eui.elastic.co/pr_3167/

[cchaos]

LGTM, though I think the PR is out of date with master as the Changelog is incorrect.

[kibanamachine]

Preview documentation changes for this PR: https://eui.elastic.co/pr_3167/