Log errors during construction

[feltech]

What

Log any errors during construction of the Ar2 plugin

Why

Currently we allow exceptions to propagate if they occur in the constructor of the plugin.

However, since plugins are/can be instantiated deep inside USD lazily when the registry is first accessed (i.e. SdrRegistry::GetInstance() ), if an application isn't aware that plugins are loading and can throw exceptions, then any error might just be swallowed and lead to hard-to-debug issues.

This came about whilst prototyping our Ar2 shim plugin in Katana, triggering a misleading error loading Katana's USD RenderInfo plugin, caused, ultimately, by a Python exception in BAL(!).

[feltech]

We should log at debug level, so that it isn't printed byu default, since the host application should be the one reporting these errors.