Store oval result sources to a map instead of disposing them
Do not free string when you need to allocate it again.
Make sure that oscap_source is added to the table.
Refactor: Extract function: _build_oval_result_sources
Export all oval results at once, after sources are prepared.
We cannot use realpath easily, we need to play guessing game

Previously, we avoided duplicates just by calling realpath.
But realpath only works for exisiting files. We changed export
code and we no longer have files exported, but we still need
to avoid duplicates.
Refactor: Extract function: xccdf_benchmark_export_source
Use oscap_source to export XCCDF results from session.
Validate XCCDF results using oscap_source
Do not export namespaced property by xmlNewProp

Use xmlNewNsProp instead.

Addressing (pre-export validation error):
OpenSCAP Error: File '/tmp/tmp.k8sAMVDRGW' line 0: Element '{http://checklists.nist.gov/xccdf/1.1}Benchmark', attribute 'xml:lang': The attribute 'xml:lang' is not allowed. [xccdf_session.c:350]
Could not export OVAL Results correctly to /tmp/tmp.k8sAMVDRGW [xccdf_session.c:1020]