Update all the default parameters after an instantiation (#8689)

The old implementation relied on the (now?) wrong assumption that
default-valued parameters can only be placed after the required ones.

Fixes #8683

tests/proc/t8683.nim

@@ -0,0 +1,11 @@
+discard """
+  output: "1"
+"""
+
+proc foo[T](bar: proc (x, y: T): int = system.cmp, baz: int) =
+  echo "1"
+
+proc foo[T](bar: proc (x, y: T): int = system.cmp) =
+  echo "2"
+
+foo[int](baz = 5)