Flow: do not remove child items from the DOM when drilling

[benelan]

Description

Update calcite-flow to no longer remove a calcite-flow-item from the DOM when drilling. Instead, a selected property should be added to calcite-flow-item to determine which item is actively visible instead of assuming the last child item in a flow wins. The calcite-flow will be updated to look at the selected property of a calcite-flow-item.

Acceptance Criteria

• Flow Items are no longer removed from the DOM when drilling.
• New selected property on Flow Item is used instead

Relevant Info

blocked until #5071 is completed

Which Component

calcite-flow
calcite-flow-item

Example Use Case

No response

[driskull]

@benelan @jcfranco Is this something we want to do pre 1.0?

If we add an open property to the flow-item, to support it in flow we would also probably need to add an open property to panel which I don't think we want to do. Introducing a new open property and immediately deprecating it doesn't sound like a great idea.