fix(core): handle primitive children on reconstruct

[CodyJasonBennett]

Swaps over R3F-managed children of primitives when reconstructing. This lets their object prop predictably keep declarative children.

<primitive object={foo ? object1 : object2}>
  <mesh />
  <material />
</primitive>

[codesandbox-ci]

This pull request is automatically built and testable in CodeSandbox.

To see build info of the built libraries, click here or the icon next to each commit SHA.

Latest deployment of this branch, based on commit 6186465:

Sandbox	Source
example	Configuration