notation3 doesn't support unparenthesized multiple binders like Π₀ i j, δ i j

[Komyyy]

This issue was found out in #13198.
The scoped binders in notation3 doesn't support unparenthesized multiple binders like Π₀ i j, δ i j.
The notation Π₀ i, β i is defined by the notation3 command, as notation3 "Π₀ "(...)", "r:(scoped f => DFinsupp f) => r.
When we use multiple binders on the notation3, we must parenthesize them like Π₀ (i) (j), δ i j. The parser doesn't recognize Π₀ i j, δ i j.
This is regression from Lean 3.