MethodInfo refactoring

Differentiating between Signals and Methods at the DOM API level, using kindValue (DomType), can be beneficial in certain contexts, such as the qmlls DocumentSymbol request (Outline). The formatting also varies significantly based on MethodType, with notable differences between Signals and Methods. Since Signals are fundamentally distinct constructs from Methods, some cases, like the qmlls DocumentSymbols request, could benefit from having their own "available" signature handling.

These points raise several considerations:

• Should Signals and Methods be separated? For instance, should we keep only method/function-related elements within MethodInfo and move Signal-related functionality to a dedicated Signal structure?
• Should we introduce a unified mechanism for storing and retrieving signatures? (For example adding a new member to MethodInfo, which is filled by QQmlDomAstCreator)
• If Signals and Methods remain under MethodInfo,  we  should better unify / refactor output methods (e.g., writeOut) and parameter handling
• Do Signals and Methods have more differences than similarities, suggesting the need for a clearer separation?