fix(Tooltip): bring focus/blur handlers back (#3633)
fix(Tooltip): bring focus/blur handlers back (#3633)

This change brings back focus/blur handling code that was inadvertently
removed. This change also renames `_debouncedHandleHover` private
method to better represent what the latest code does.

Fixes #3601.
carbon-design-system/carbon-components,carbon-design-system/carbon-components,carbon-design-system/carbon-components