[Array API] Add linalg.vecdot (#70542)
This PR adds the function `linalg.vecdot` specified by the [Array
API](https://data-apis.org/array-api/latest/API_specification/linear_algebra_functions.html#function-vecdot)
For the complex case, it chooses to implement \sum x_i y_i. See the
discussion in https://github.com/data-apis/array-api/issues/356
Edit. When it comes to testing, this function is not quite a binopt, nor a reduction opt. As such, we're this close to be able to get the extra testing, but we don't quite make it. Now, it's such a simple op that I think we'll make it without this.
Resolves https://github.com/pytorch/pytorch/issues/18027.
cc @mruberry @rgommers @pmeier @asmeurer @leofang @AnirudhDagar @asi1024 @emcastillo @kmaehashi
Pull Request resolved: https://github.com/pytorch/pytorch/pull/70542
Approved by: https://github.com/IvanYashchuk, https://github.com/mruberry
