[ConstraintSystem] Add index value (as an impact of the score kind) to output of debug constraints.

[kntkymt]

Environment

swift-driver version: 1.115 Apple Swift version 6.0 (swiftlang-6.0.0.9.10 clang-1600.0.26.2)
Target: arm64-apple-macosx14.0

Motivation

resolve #72842

As I mentioned in #72842,
In current output of debug-constraints, We cannot easily recognize which score is more impactful.

class Animal {}
class Cat: Animal {}
func f(_ a: [Cat?]) { }
func f(_ a: [Any]) { }

let a: [Cat] = [Cat()]
f(a)

// swiftc -Xfrontend -debug-constraints Source.swift

---Solver statistics---
--- Solution #0 ---
Fixed score: [component: collection upcast conversion(s), value: 1] [component: value to optional promotion(s), value: 1]
...

--- Solution #1 ---
Fixed score: [component: collection upcast conversion(s), value: 1] [component: empty-existential conversion(s), value: 1]
...

---Solution---
Fixed score: [component: collection upcast conversion(s), value: 1] [component: empty-existential conversion(s), value: 1]
...

Full Output

We cannot recognize which score is more/less impactful. e.g. between value to optional promotion of Solution#0 and empty-existential conversion of Solution#1.
(We can guess empty-existential conversion(s) is less impactful, since final Solution is Solution#1 but it is ambiguous.)

Proposed Solution

I added number indicating impact of score to output of debug-constraints.
Currently I used index of enum ScoreKind. (i.e. smaller number is more impactful).

// swiftc -Xfrontend -debug-constraints Source.swift

---Solver statistics---
--- Solution #0 ---
Fixed score: [component: #14 collection upcast conversion(s), value: 1] [component: #15 value to optional promotion(s), value: 1]
...

--- Solution #1 ---
Fixed score: [component: #14 collection upcast conversion(s), value: 1] [component: #16 empty-existential conversion(s), value: 1]
...

---Solution---
Fixed score: [component: #14 collection upcast conversion(s), value: 1] [component: #16 empty-existential conversion(s), value: 1]
...

Alternative Format

Suggestion for other formats are welcome.

e. g.

// reversed index (i.e. bigger number is more impactful)
[component: #8 collection upcast conversion(s), value: 1]

// added label as well (I'm not sure whether "rank" is correct wording or not tho)
[rank: 14, component: collection upcast conversion(s), value: 1]

[xedin]

Thanks! I think to clarify this even further we should use weight instead of index (which is opposite) and instead of value: -> impact:. This would better reflect the meaning of these values.