Refine handling of pattern binders for large tuples

[odersky]

Extracted from the named tuples PR, where it allowed the correct typing of

val bob = (
  x0 = 0, x1 = 0, x2 = 0, x3 = 0, x4 = 0, x5 = 0, x6 = 0, x7 = 0, x8 = 0, x9 = 0,
  name = "Bob", y1 = 0, age = 33, y2 = 0,
  z0 = 0, z1 = 0, z2 = 0, z3 = 0, z4 = 0, z5 = 0, z6 = 0, z7 = 0, z8 = 0, z9 = 0)

  bob match
    case p @ (name = "Bob", age = a) =>
      p,age

The problem was that p was typed before as <some large tuple type> & TupleXXL and that prevented the correct analysis of tuple elements.

I am submitting this as a separate PR since it might also be relevant for #19084.