[minor] sigmatch errors should be sorted, for reproducible errors

[timotheecour]

I ran into this situation a few times; #13536 is also affected by it. sigmatch errors should be sorted so that unrelated code changes don't change such messages, which avoids having to re-write some tests

Example

• before fix operators containing percent for VM usage #13536
  tests/concepts/t3330.nim test shows this:

t3330.nim(78, 4) Error: type mismatch: got <Bar[system.int]>
but expected one of:
proc test(foo: Foo[int])
  first type mismatch at position: 1
  required type for foo: Foo[int]
  but expression 'bar' is of type: Bar[system.int]
t3330.nim(63, 8) Hint: Non-matching candidates for add(k, string, T)
proc add(x: var string; y: string)
  first type mismatch at position: 1
  required type for x: var string
  but expression 'k' is of type: Alias
proc add[T](x: var seq[T]; y: openArray[T])
  first type mismatch at position: 1
  required type for x: var seq[T]
  but expression 'k' is of type: Alias
proc add(x: var string; y: cstring)
  first type mismatch at position: 1
  required type for x: var string
  but expression 'k' is of type: Alias
proc add[T](x: var seq[T]; y: T)
  first type mismatch at position: 1
  required type for x: var seq[T]
  but expression 'k' is of type: Alias
proc add(result: var string; x: float)
  first type mismatch at position: 1
  required type for result: var string
  but expression 'k' is of type: Alias
proc add(x: var string; y: char)
  first type mismatch at position: 1
  required type for x: var string
  but expression 'k' is of type: Alias
proc add(result: var string; x: int64)
  first type mismatch at position: 1
  required type for result: var string
  but expression 'k' is of type: Alias

t3330.nim(63, 8) template/generic instantiation of `add` from here
t3330.nim(70, 6) Foo: 'bar.value' cannot be assigned to
t3330.nim(63, 8) template/generic instantiation of `add` from here
t3330.nim(71, 6) Foo: 'bar.x' cannot be assigned to

expression: test(bar)'''

• after fix operators containing percent for VM usage #13536
  some entries are shuffled.

Expected Output

entries remain in the same order

Possible Solution

• simply sort (by cmp[string]) the error messages for each sigmatch candidate