Add tensor.m(mask) operator

[jerry73204]

This patch adds a tensor.m(mask) operator. The mask can be a tensor or a boolean slice/array.
It depends on a previous PR #790 that is still under review.

let x: Tensor = vec![1i64, 2, 3, 4].try_into().unwrap();
let y = x.m([true, false, false, true]);  // [1, 4]