[cxxmodules] Keep the pending rdict files to be re-read on reload.
[cxxmodules] Keep the pending rdict files to be re-read on reload.

When a library is re-loaded (via .L) we should reload the corresponding rdict
file. However current ROOT (without modules) just re-reads the rdict file.

This patch brings this behavior for modules and is intended to be a quick fix
for the os nightly failures of kind:

Error in TCling::LoadPCM: ROOT PCM /.../libTree_rdict.pcm file does not exist
Info in TCling::LoadPCM: In-memory ROOT PCM candidate /.../libASImageGui_rdict.pcm
Info in TCling::LoadPCM: In-memory ROOT PCM candidate /.../libASImage_rdict.pcmError in TCling::LoadPCM: ROOT PCM /.../libTree_rdict.pcm file does not exist
Info in TCling::LoadPCM: In-memory ROOT PCM candidate /.../libASImageGui_rdict.pcm
Info in TCling::LoadPCM: In-memory ROOT PCM candidate /.../libASImage_rdict.pcm

The continuation of this work is in root-project/root#5420

karies/root,karies/root,olifre/root,olifre/root,karies/root,root-mirror/root,karies/root,olifre/root,root-mirror/root,karies/root,root-mirror/root,root-mirror/root,karies/root,karies/root,olifre/root,root-mirror/root,olifre/root,olifre/root,karies/root,olifre/root,root-mirror/root,olifre/root,olifre/root,root-mirror/root,olifre/root,root-mirror/root,karies/root,karies/root,olifre/root,karies/root,root-mirror/root,root-mirror/root,root-mirror/root