Support french notation for vector

[junior radish]

Hello, in France we often use the following notation to display the coordinates of a point/vector, with a left bar but without right bar (see attached screenshot). It would be great if it was an option in the vector command, see https://typst.app/docs/reference/math/vec/

[hoary belfry]

You can implement something like that with a function, if you don't someone else will soon enough 😉