...as the implicitly defined copy operations would just copy the m_p* member
pointers.  Needed some modification of the ParserCleanup class so that Entity
(which has a XMLFile2UTFConverter member) can be std::move'd into
SaxExpatParser_Impl::pushEntity.

Found by new -Wdeprecated-copy of GCC trunk towards GCC 9.

Change-Id: I0cb5b5dbcd55249b475ed74b4ac6bcb12f20f2c6
Reviewed-on: https://gerrit.libreoffice.org/56453
Tested-by: Jenkins
Reviewed-by: Stephan Bergmann <sbergman@redhat.com>