XWIKI-13639: Automatically recreate Solr index when needed during upgrade

.gitignore

.../xwiki-platform-search/xwiki-platform-search-solr/pom.xml

.../org/xwiki/search/solr/internal/EmbeddedSolrInstance.java

...solr/internal/EmbeddedSolrInstanceInitializationTest.java

.../xwiki/search/solr/internal/SolrInstanceProviderTest.java

...form-search-solr-api/src/test/resources/solrhome/solr.xml

...lr-api/src/test/resources/solrhome/xwiki/conf/elevate.xml

...api/src/test/resources/solrhome/xwiki/conf/managed-schema

...api/src/test/resources/solrhome/xwiki/conf/solrconfig.xml

...olr-api/src/test/resources/solrhome/xwiki/core.properties