[Accordion] Need support in controlling the expand/collapse behaviour of Accordion panel on the consumer end.

[shantanunirale]

Need support in controlling the expand/collapse behaviour of Accordion panel on the consumer end. May be taking inputs from consumer before expand or collapse operation. The consumer should be able to stop default behaviour of intended operation e.g. stop expand, stop collapse.

Adding support for callback function, may be a function returning a Promise on ClrAccordionPanel which would be called before collapsing any accordion panel. If the consumer resolves the promise it will collapse the panel otherwise panel will be kept open.

For example,
We have a use case where before closing any panel user need to check if anything inside the panel content is in progress/not in committed state. May be user need to show some confirmation before user tries to close it as the current state will be lost.