Auto merge of #113847 - SparrowLii:path_clone, r=cjgillot

avoid clone path prefix when lowering to hir

Found this while trying to parallelize `lower_to_hir`.

When lowering to hir, `Nested` paths in `ast` will be split and the prefix segments will be cloned. This could be omited, since the only consequence is that the prefix segments in `Path`s in hir will have the same `HirId`s, and it seems harmless.

This simplifies the process of lowering to hir and avoids re-modification of `ResolverAstLowering`.

r? `@Aaron1011`
cc #99292

Author: bors