[EuiDatePicker] Fix `inline` rendering + add `append`/`prepend` support

[cee-chen]

Summary

I discovered an inline EuiDatePicker border regression while investigating #5958, and I also discovered some very incorrect usages of EuiFormControlLayout while grepping for the component in Kibana.

Adding append/prepend nodes to EuiDatePicker will help with a significant amount of those use cases, as people were using the layout wrapper just for appending/prepending info to the date picker input.

QA

• Go to https://eui.elastic.co/pr_7987/#/forms/date-picker#date-picker-inline
• [ ] Both inline date pickers should not have a border when the Show shadow switch is toggled

Before	After

• Go to https://eui.elastic.co/pr_7987/#/forms/date-picker#date-picker-states or https://eui.elastic.co/pr_7987/storybook/?path=/story/forms-euidatepicker--playground
• [ ] Toggling the append/prepend display should render side nodes as expected, e.g.

General checklist

• Browser QA
  • [x] Checked in both light and dark modes
  • [x] Checked in mobile
  • [x] Checked in Chrome, Safari, Edge, and Firefox ~- [ ] Checked for accessibility including keyboard-only and screenreader modes~
• Docs site QA
  • [x] Updated documentation
  • [x] Props have proper autodocs (using @default if default values are missing) and playground toggles ~- [ ] Checked Code Sandbox works for any docs examples~
• Code quality checklist
  • [x] Added or updated jest ~and cypress~ tests ~- [ ] Updated visual regression tests~
• Release checklist
  • [x] A changelog entry exists and is marked appropriately. ~- [ ] If applicable, added the breaking change issue label (and filled out the breaking change checklist)~
• Designer checklist - N/A

[elasticmachine]

:green_heart: Build Succeeded

• Buildkite Build
• Commit: 023671705868d0fdd92e715c2d1e877278032819

History

• :green_heart: Build #2651 succeeded 4685c696a7b717e1c9dcec24c40751d5994939e3