Add tooltipContent and tooltipProps support for EuiComboBox and EuiSelectable options

[JasonStoltz]

Requested by the Cloud team to replace long description text for roles. They would like to ship this by the end of the month.

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See similar existing APIs:

eui/src/components/button/button_group/button_group.tsx

Lines 56 to 63 in f10c46d

	/**
	* Optional custom tooltip content for the button
	*/
	toolTipContent?: EuiToolTipProps['content'];
	/**
	* Optional props to pass to the underlying **[EuiToolTip](/#/display/tooltip)**
	*/
	toolTipProps?: Partial<Omit<EuiToolTipProps, 'content' | 'children'>>;

eui/src/components/context_menu/context_menu_item.tsx

Lines 47 to 55 in 68439d3

	/**
	* Required if using a tooltip. Add an optional tooltip on hover
	*/
	toolTipContent?: ReactNode;
	/**
	* Optional configuration to pass to the underlying [EuiToolTip](/#/display/tooltip).
	* Accepts any prop that EuiToolTip does, except for `content` and `children`.
	*/
	toolTipProps?: Partial<Omit<EuiToolTipProps, 'content' | 'children'>>;

Tooltips should also be toggled by keyboard "focus" (which isn't true focus in the case of EuiSelectable)

[JasonStoltz]

@cee-chen Do you have more context to link here?

[cee-chen]

Original design that tooltips are intended to replace:

The tooltips replace the non-essential descriptions and will gain back valuable screen real estate.

[cee-chen]

Scope of work:

API considerations:

• API should go on the option object/type, not on the top-level component
• It should be possible for mixed usage (i.e., some options to have tooltip content and some options to not have tooltips).
• Please start with adding the new prop to EuiComboBox first (higher priority). EuiSelectable is nice to have and will be needed for [EuiComboBox] Rebuild with EuiSelectable #2841, but can also wait if needed.

UX considerations:

• Triggering the tooltip on keyboard "focus" is going to require some amount of trickery/workaround as focus is technically on the search input and not on the actual list item. If this is too complicated to do, let's punt it to a separate follow-up PR and focus on mouse functionality first.
• Default tooltip delay to short and not long, please (per recent conversations with Marcialis)
• (OPTIONAL) We may want to consider automatically rendering the iInCircle icon if tooltipContent exists and has been passed, to let users know that the content exists. Would be open to thoughts on this or if we should just let users decide this themselves via the append or prepend properties