Teaching Popover PR Feedback

[behowell]

This issue is tracking the resolution of outstanding comments from PR feat(react-teaching-popover-preview): Core functionality

Unresolved comments from @layershifter:

• [ ] Use images from CDN in examples
• [ ] Fix use of renderByDefault in useTeachingPopoverHeader
• [ ] Consider changing TeachingPopoverButton.buttonType prop
• [ ] Consider changing TeachingPopoverButton.altStepText prop
• [ ] Remove Paritial<> around slots type for TeachingPopoverPageCountProps
• [ ] Don't use render props: TeachingPopoverPageCountChildRenderFunction
• [ ] Rename useTeachingPopoverContext.ts to useTeachingPopoverContextValues.ts
• [ ] Add defaultCurrentPage prop to TeachingPopover
• [ ] Update useTeachingPopoverContextValues to match what's in renderTeachingPopover, and use contextValues.teachingPopover in the render function
• [ ] Remove TeachingPopoverTitle.showDismiss prop because it's redundant with dismissButton={null}

Unresolved comments from @behowell:

• [ ] renderTeachingPopoverPageCount shouldn't return null
• [ ] TeachingPopoverPageCount shouldn't render its carouselIcon slot multiple times