SOLR-17959: Add alwaysStopwords option to edismax

[andywebb1975]

https://issues.apache.org/jira/browse/SOLR-17959

Description

We were surprised by edismax's behaviour for pure-stopword queries, having expected that these would return zero results. Its 'If a query consists of all stopwords, such as "to be or not to be", then all words are required.' behaviour is the opposite to what we want as we're using query-time stopwords to prevent particular query terms matching, but there's no way to disable the behaviour other than using dismax instead, which has other impacts.

Solution

This PR adds an alwaysStopwords option that disables the default behaviour, enabling stopwords to be always ignored.

Tests

I've added tests for the default and new behaviours.

Checklist

Please review the following and check all that apply:

• I have reviewed the guidelines for How to Contribute and my code conforms to the standards described there to the best of my ability.
• I have created a Jira issue and added the issue ID to my pull request title.
• I have given Solr maintainers access to contribute to my PR branch. (optional but recommended)
• I have developed this patch against the main branch.
• I have run ./gradlew check.
• I have added tests for my changes.
• I have added documentation for the Reference Guide