fix(IconButton): adds hasIconOnly classname to fix right padding

[jnm2377]

Closes #11295

Changelog

• IconButton now uses cds--btn--icon-only and passes in a className prop
• adds margin to the IconButton story so the tooltip wouldn't be overflowing

Testing / Reviewing

1. View IconOnly story
2. test the playground knobs for size & kind
3. spacing should work correctly now (square btn not rectangle)

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