respect destination syntax of table 8.2 in PDF 1.6 specs

Looking at section 8.2 of PDF 1.6 specs, Document-Level Navigation (used for bookmarks/outline) requires a /Dest declaration.

Currently, PyPDF2 output when merging PDFs looks like :
```
30 0 obj
<<
/Parent 29 0 R
/Next 31 0 R
/Title (Test)
/Left 85.03937
/Type /XYZ
/Prev 28 0 R
/Top 643.46457
/Zoom 0
/Page 9 0 R
>>
```

Instead of : 
```
30 0 obj
<<
/Parent 29 0 R
/Prev 28 0 R
/Next 31 0 R
/Title (Test)
/Dest [9 0 R /XYZ 85.03937 643.46457 0]
>>
```