SOLR-18023: Mapping field module

[igiguere]

https://issues.apache.org/jira/browse/SOLR-18023

Description

This module adds a new field type, and a new QParserPlugin, to index and search key-value mappings as a value of a user-defined field.

Solution

Class MappingType extends AbstractSubTypeFieldType, and allows for sub-fields of different types. Primitive field types are supported as "key" and "value" of mappings.

Class MappingsQParserPlugin, and class MappingsQParser provide support for local params to search into the values of the key-value pairs.

Configuration and usage documentation added in solr-ref-guide/modules/query-guide/mapping-field.adoc

Tests

Unit tests in TestMappingType and TestMappingsQParserPlugin

Functionnal tests using an installation of Solr 9.10, to which was added the lib solr-mapping-field-11.0-SNAPSHOT.jar, and required configuration.

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, not available for branches on forks living under an organisation)
• [*] 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
• [*] I have added a changelog entry for my change