Fix and improve some errors and exceptions

[TPGamesNL]

Description

• Fix code like add awdwadwa to {_x} not giving the proper error
• Improve hook loading exception handling
• Improve variable serialization exception handling
• Improve 'no class info found for ...' errors by including pattern and element class
• Remove a wrongful assert

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Target Minecraft Versions: any
Requirements: none
Related Issues: #4224 (non-fixing), #4234

[TheLimeGlass]

Can this be merged soon? I actually use this for error checking, it's helpful. @APickledWalrus

[TheLimeGlass]

Skript.zip
Here is a compiled jar. It's zipped so I can upload it here (GitHub doesn't support .jar) for anyone that wants to help test this, or are too lazy to compile and build :P

[TheLimeGlass]

I did have an error where it printed the same package location and same syntax for two different syntaxes both with incorrect classinfos expressions, maybe the local variable is not getting reset on loop somewhere?

Also I don't know if this is possible without some reflection, but it would be nice to document in the error where the calling code location for the .register is.