Method create_next_table

Internal helper function to create the page table of the next level if needed. If the passed entry is unused, a new frame is allocated from the given allocator, zeroed, and the entry is updated to that address. If the passed entry is already mapped, the next table is returned directly. Returns `MapToError::FrameAllocationFailed` if the entry is unused and the allocator returned `None`. Returns `

(
        &self,
        entry: &'b mut PageTableEntry,
        insert_flags: PageTableFlags,
    )