[DF] Add internal function to retrieve tree info

[vepadulano]

This could be a useful thing to have around for internal use. For example, this could enable in distrdf creating directly an RDF object in the headnode, then querying the list of tree/file names from it

[phsft-bot]

Starting build on ROOT-debian10-i386/soversion, ROOT-performance-centos8-multicore/cxx17, ROOT-ubuntu18.04/nortcxxmod, ROOT-ubuntu2004/python3, mac1015/cxx17, mac11/cxx14, windows10/cxx14 How to customize builds

[phsft-bot]

Build failed on windows10/cxx14. Running on null:C:\build\workspace\root-pullrequests-build See console output.

Failing tests:

• projectroot.roottest.root.io.transient.base.roottest_root_io_transient_base_WriteFile
• projectroot.roottest.root.io.transient.base.roottest_root_io_transient_base_hadd_autoload

[phsft-bot]

Starting build on ROOT-debian10-i386/soversion, ROOT-performance-centos8-multicore/cxx17, ROOT-ubuntu18.04/nortcxxmod, ROOT-ubuntu2004/python3, mac1015/cxx17, mac11/cxx14, windows10/cxx14 How to customize builds

[phsft-bot]

Build failed on ROOT-performance-centos8-multicore/cxx17. Running on olbdw-01.cern.ch:/data/sftnight/workspace/root-pullrequests-build See console output.

Failing tests:

• projectroot.runtutorials.tutorial_roostats_rs401c_FeldmanCousins

[phsft-bot]

Starting build on ROOT-debian10-i386/soversion, ROOT-performance-centos8-multicore/cxx17, ROOT-ubuntu18.04/nortcxxmod, ROOT-ubuntu2004/python3, mac1015/cxx17, mac11/cxx14, windows10/cxx14 How to customize builds

[phsft-bot]

Starting build on ROOT-debian10-i386/soversion, ROOT-performance-centos8-multicore/cxx17, ROOT-ubuntu18.04/nortcxxmod, ROOT-ubuntu2004/python3, mac1015/cxx17, mac11/cxx14, windows10/cxx14 How to customize builds

[phsft-bot]

Build failed on windows10/cxx14. Running on null:C:\build\workspace\root-pullrequests-build See console output.

Errors:

• [2022-08-01T13:56:11.276Z] LINK : fatal error LNK1104: cannot open file 'C:\build\workspace\root-pullrequests-build\build\bin\libCore.dll' [C:\build\workspace\root-pullrequests-build\build\core\Core.vcxproj]

[phsft-bot]

Build failed on ROOT-performance-centos8-multicore/cxx17. Running on olbdw-01.cern.ch:/data/sftnight/workspace/root-pullrequests-build See console output.

Failing tests:

• projectroot.runtutorials.tutorial_roostats_rs102_hypotestwithshapes
• projectroot.runtutorials.tutorial_spectrum_Background_order
• projectroot.runtutorials.tutorial_spectrum_Background_incr
• projectroot.runtutorials.tutorial_roostats_rs_numberCountingCombination
• projectroot.runtutorials.tutorial_spectrum_Background_gamma64

[phsft-bot]

Starting build on ROOT-debian10-i386/soversion, ROOT-performance-centos8-multicore/cxx17, ROOT-ubuntu18.04/nortcxxmod, ROOT-ubuntu2004/python3, mac1015/cxx17, mac11/cxx14, windows10/cxx14 How to customize builds