feat(Popper): made inline logic internal to Popper

[thatblindgeye]

What: Closes #8673

Changes needed from the current PRs:

• Date picker (#8636)
  • remove the inputGroupRef from line 123
  • Remove getInlineParentElement or revert it to the original getParentElement on line 201 (depends if we find it necessary anymore; if we revert it then "parent" needs to be added back to the prop types)
  • update line 246 where appendTo is passed a value; if we revert line 201 then this line can also be reverted, otherwise we can just make it appendTo={appendTo}
  • Remove the innerRef on line 250
• LabelGroup demo (#8630)
  • Remove the appendTo from line 121
• Nav flyout (#8628) is good as-is. Moving the popper menu contents to inside the <li> element will require investigating how popper-core sets the transform: translate property.
• Popover (#8621) can mostly be reverted, but keep the default value as appendTo = "inline"
• Composable menu demos (#8623): remove the appendTo prop from the examples

Original comment explaining the motivation

Essentially makes the logic for "inline" popper internal to Popper itself, rather than the components using Popper (Tooltip, Popover, Date Picker, etc) needing to house that logic (sometimes in different ways). For the most part this would only require another component to pass appendTo="inline" to Popper rather than needing to use a ref or call a function to determine it.

Using Popover as an example, the markup from this setup looks like this (using the children prop):

Or like this (using reference, though the resulting markup would depend if there's any other content between the trigger and the <Popover>):

I did try a slightly different setup locally, where if appendTo === "inline" then the popper contents would render inside of the trigger's wrapper <div style="display: contents"..., so might depend if anyone has a preference. The markup from this other approach ended up like this using the children prop on Popover:

The Nav Flyout would be an outlier in that it either would need the logic implemented in #8628, or moving the flyout menu inside of the <li> within NavItem (doing this would require looking into how the transform: translate styling is applied to Popper via computedStyles in popper-core).

Additional issues:

[thatblindgeye]

cc @nicolethoen @kmcfaul @wise-king-sullyman

[patternfly-build]

Preview: https://patternfly-react-pr-8669.surge.sh

A11y report: https://patternfly-react-pr-8669-a11y.surge.sh