chameleon-accordions behave unexpectedly when manually manipulated

[ryuhhnn]

Describe the bug
The logic in chameleon-accordions behaves unexpectedly if the slotted children are manually manipulated. This is due to the fact that indices for the slotted children are only assigned on first render. An event listener needs to be added in chameleon-accordions to recalculate the indices whenever the slotted children change: https://developer.mozilla.org/en-US/docs/Web/API/HTMLSlotElement/slotchange_event