In SSR, Store Elements of Composites on the Stack for Warnings (#10187)

In DEV mode this keeps an additional sub-stack within the stack of the
server renderer. This substack keeps track of all the elements that we
resolved to get to to the next processing frame.

This lets us recreate the full composite component stack for warnings.
Normally the stack only contains host components.

We reset this every time we're going to resolve another sibling.