Class URSymbolAbstract

Legacy base class for all symbol entities from the original symbol model.

DEPRECATION: The new symbol model uses plain TypeScript interfaces instead of an inheritance hierarchy. Replace usages with the appropriate interface from @universal-robots/contribution-api/types/symbols. Example migration:

• class URVariable extends URSymbol { ... } -> use VariableDeclaration for declarations and store runtime state in VariableDescription.
• Type guards should be replaced by the new interface-specific guards (e.g. isVariableDeclaration).