DefaultSearchPlugin: Product can be falsely indexed as in stock if a deleted variant has stock

[kyunal]

Describe the bug
Consider a product with multiple variants where one variant, that had stock, was deleted after some time. The DefaultSearchPlugin will falsely index that the product is in stock as it does not pay attention to the soft-deleted variant.

To Reproduce
Steps to reproduce the behavior:

1. Create a product with multiple variants, put one in stock that you intend to soft delete
2. Delete said variant
3. According to the DefaultSearchPlugin the product is falsely in-stock

Expected behavior
The product should be shown out of stock and the deleted variant should be disregarded

Environment (please complete the following information):

• @vendure/core version: 2.3.0 but I found that this affects later versions too
• Nodejs version 18
• Database (mysql/postgres etc): postgres 16

Additional context
I will PR this later in the day