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Digit antitranspose

Convert a matrix or grid of digits to its antitranspose. For a square matrix , this is its reflection in its [antidiagonal](https://en.wikipedia.org/wiki/Main_diagonal#Antidiagonal "Antidiagonal on Wikipedia"). More generally, for a rectangular matrix, this is its reflection in its [skew diagonal](https://mathworld.wolfram.com/SkewDiagonal.html "Skew diagonal on Wolfram").

Less formally, the line to reflect in is from South West to North East, at 45 degrees regardless of the proportions of the rectangle.

## Input
- A (not necessarily square) matrix or grid of single digit non-negative numbers
- This may be a matrix or any 2 dimensional data structure or a 1 dimensional data structure along with width and/or height, or a sequence of 1 dimensional data structures representing rows
- The width and height will always be at least 1 (the grid will never be empty)
- The single digit numbers contained in this data structure may be of number types or characters or single character strings
- For example, the input may be a string of numeric characters with delimiters between rows

## Output
- The same data structure type as the input
  - This applies to every nested level: if the input is a list of strings of characters, the output must be a list of strings of characters
- Each digit in the input is moved:
  - from (x, y) to (height - y - 1, width - x - 1) (if zero indexed from top left)
  - from (x, y) to (height - y + 1, width - x + 1) (if one indexed from top left)

## Examples
Here input and output are represented as newline separated strings of characters. You can check that the input and output match by holding a reflective surface such as a mirror or phone screen at 45 degrees next to the input. The reflected numbers won't be upright but they will be in the same locations as the output.

### Square input
```text
012
345
678
```

### Square output
```text
852
741
630
```

### Rectangular input
```text
01
23
45
67
```

### Rectangular output
```text
7531
6420
```

## Test cases
Test cases are in the format `"input" : "output"` where the input and output are strings containing comma separated rows. For comparison, the first 2 test cases are the same as the examples shown above.

```text
"012,345,678" : "852,741,630"
"01,23,45,67" : "7531,6420"
"0" : "0"
"12" : "2,1"
"3,4" : "43"
"56,78" : "86,75"
```

> Explanations are optional, but I'm more likely to upvote answers that have one.