Ignore Ice.Plugin.IceSSL for compatibility with 3.7

[pepone]

What will happen if the user keep this property in his config file? Do we have any validation of plug-in names with an Ice prefix?

Originally posted by @bernardnormier in https://github.com/zeroc-ice/ice/pull/2388#pullrequestreview-2154678837

We should review, but I think we should probably ignore the property.

[externl]

There are already lots of property changes: we're removing deprecated properties, old irrelevant properties, etc. I don't think we should specially ignore a single property just for version sharing.

IMO if you use Ice.Plugin.IceSSL with 3.8 you should get a warning, assuming we have check for Ice.Plugin.XXX

[bernardnormier]

My understanding is IceSSL remains a plugin in Ice 3.8, just like TCP is a plugin, UDP is a plugin etc.

https://github.com/zeroc-ice/ice/blob/d6e44874ca8d6892f96a6b7b07fcba08b7bb47e2/cpp/include/Ice/RegisterPlugins.h#L48

So presumably Ice.Plugin.IceSSL=1 should be valid, just like Ice.Plugin.IceUDP=1 is valid.

[bernardnormier]

I verified it works fine in C++.