Fix ToggleGroup children prop handling to avoid crashing with non-element children

[dvail]

What: Closes #8877

Fixes the runtime error by using React's builtin isValidElement() before accessing the type property of the child value.

[patternfly-build]

Preview: https://patternfly-react-pr-8986.surge.sh

A11y report: https://patternfly-react-pr-8986-a11y.surge.sh

[nicolethoen]

@gitdallas will this require a codemod as well to at least give the users a warning that the type has changed?

[gitdallas]

It doesn't look to me like this should break or even cause tests/snaps/selectors to fail on any existing code as if this was failing before no one would be using it this way?

I don't think we need a codemod here unless you think it's worth pointing out that it now works with non-element children. @nicolethoen

[dvail]

Agreed, the only case I can think of (which is what we hit on ACS) is if a user was conditionally rendering these children with a snippet like:

{shouldRender && <ToggleGroupItem {...props } />}

where shouldRender is almost always true, but is false in rare edge cases that aren't covered by tests. In our case this was noticed immediately but I could imagine this popping up unexpectedly for someone else.