In Scala 3: handle extension methods and future proof for SIP-47

[MateuszKubuszok]

methodSymbol.paramSymss would return List[List[Symbol]] where type parameters - if present - are always the first nested List. However, this is not true for extension methods - listed as methods of the type but with different type order! - and in the future it will not not be true for methods with clause interleaving.

All usages of paramsSymss should be adapted to not assume that type-symbol list is always as the at first place and only there. (Additionally, code should ideally handle mutiple empty parameter lists).