Add ParamClause to allow multiple type param clauses

[nicolasstucki]

Reflects the changes done in #10940

Based on Subsumes #11082

Introduces ParamClause

    /** A parameter clause `[X1, ..., Xn]` or `(x1: X1, ..., xn: Xx)`
     *
     *  `[X1, ..., Xn]` are reresented with `TypeParamClause` and `(x1: X1, ..., xn: Xx)` are represented with `TermParamClause`
     *
     *  `ParamClause` encodes the following enumeration
     *  ```scala
     *  enum ParamClause:
     *    case TypeParamClause(params: List[TypeDef])
     *    case TermParamClause(params: List[ValDef])
     *  ```
     */
    type ParamClause <: AnyRef

Technically, ParamClause is like an opaque type on List[ValDef] | List[TypeDef] with some extra invariants that we need to ensure.

[nicolasstucki]

Blocked by #11076

[liufengyun]

LGTM

[nicolasstucki]

Rebased on top of #11145