fix(cdk/portal): run change detection before inserting portal content

[crisbeto]

In #16407 we made some changes where we'd run change detection after transferring the portal content to the outlet, in order to handle a case where focus traps may be attached too early. This PR reverts back to triggering change detection before moving the content, because doing it after may leave behind nodes that were inserted through ViewContainerRef inside one one of the init hooks. The initial focus trap issue is resolved by delaying the attachment instead.

These changes fix another issue where we were assuming that component portals can only have one root node. This is true for most cases, except for when a sibling is inserted through ViewContainerRef.

Finally, these changes add a detectChanges call before moving the contents of a component portal for consistency between portals. Previously we were only doing in for template portals.

Fixes #20343.