How can I get the bracket joint ?

2*x + 2*y = 15

To

2*(x + y) = 15

Another example

x^2 + 2*x*y + y^2 = 10

To

(x + y)^2 = 10

How can I get the bracket joint ?

2*x + 2*y = 15

To

2*(x + y) = 15

Another example

x^2 + 2*x*y + y^2 = 10

To

(x + y)^2 = 10

We don’t have a full factorization routine yet. In these two specific cases `Polynomial.factorSquareFree`

can achieve exactly that, but I do not expect this to work reliably in all cases.

E.g. in F#:

```
open Operators
let x = symbol "x"
let y = symbol "y"
2*x + 2*y |> Polynomial.factorSquareFree x // 2*(x + y)
x**2 + 2*x*y + y**2 |> Polynomial.factorSquareFree x // (x + y)^2
```