doc/solr-schema-9: Add mandatory attribute class

Resolves: ERROR: Error CREATEing SolrCore 'dovecot':
Unable to create core [dovecot] Caused by: [schema.xml] analyzer/tokenizer:
missing mandatory attribute 'class'

doc/solr-schema-9.xml

@@ -6,7 +6,7 @@
   <fieldType name="string" class="solr.StrField" omitNorms="true" sortMissingLast="true"/>
   <fieldType name="text" class="solr.TextField" autoGeneratePhraseQueries="true" positionIncrementGap="100">
     <analyzer type="index">
-      <tokenizer name="standard" />
+      <tokenizer name="standard" class="solr.StandardTokenizerFactory"/>
       <filter name="icuFolding" />
       <filter name="wordDelimiterGraph" catenateNumbers="1" generateNumberParts="1" splitOnCaseChange="1" generateWordParts="1" splitOnNumerics="1" catenateAll="1" catenateWords="1"/>
       <filter name="flattenGraph"/>
@@ -14,7 +14,7 @@
       <filter name="porterStem"/>
     </analyzer>
     <analyzer type="query">
-      <tokenizer name="standard" />
+      <tokenizer name="standard" class="solr.StandardTokenizerFactory"/>
       <filter name="icuFolding" />
       <filter name="synonymGraph" expand="true" ignoreCase="true" synonyms="synonyms.txt"/>
       <filter name="flattenGraph" />