Fix bugs GH-16150 and GH-16152: intern document mismanagement

The reference counts of the internal document pointer are mismanaged.
In the case of fragments the refcount may be increased

Fix bugs GH-16150 and GH-16152: intern document mismanagement

The reference counts of the internal document pointer are mismanaged.
In the case of fragments the refcount may be increased too much, while
for other cases the document reference may not be applied to all
children.

This bug existed for a long time and this doesn't reproduce (easily)
on 8.2 due to other bugs. Furthermore 8.2 will enter security mode soon,
and this change may be too risky.

Fixes GH-16150.
Fixed GH-16152.
Closes GH-16178.

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