formatter: Fix constraint block expansion

[ghost]

Fix expansion of constraint declarations with flattened constraint blocks:

{ ([<auto>], policy: always-expand) @{}
  { ([<auto>], policy: fit-else-expand) @{25}, (origin: "constraint ... : 1000]};}")
    { ([constraint num_trans_c {], policy: fit-else-expand) }
    { (>>[num_trans inside { [ 800 : 1000 ] } ;], policy: always-expand, (origin: "num_trans i...0 : 1000]};")) }
    { ([}], policy: uninitialized) }
  }
}

by propagation of partition policy:

{ ([<auto>], policy: always-expand) @{}
  { ([<auto>], policy: always-expand) @{25}, (origin: "constraint ... : 1000]};}")
    { ([constraint num_trans_c {], policy: fit-else-expand) }
    { (>>[num_trans inside { [ 800 : 1000 ] } ;], policy: always-expand, (origin: "num_trans i...0 : 1000]};")) }
    { ([}], policy: uninitialized) }
  }
}

[hzeller]

LGTM.
Ready to merge once CI is through.

[ghost]

Okay, great. But let's wait for a clarification in an issue thread.