Provide a utility function to escape strings for standard Solr query syntax

It is somethings necessary to build Solr query in Velocity, and we need to be able to escape special characters: https://solr.apache.org/guide/solr/latest/query-guide/standard-query-parser.html#escaping-special-characters

Something like $escapetool.standardSolr or $escapetool.solr would be nice to have.

Note (for both a workaround and an implementation suggestion) that it should be possible to escape for solr by just adding a backslash behind each character of the string. (this doesn't work and causes org.apache.solr.common.SolrException: org.apache.solr.search.SyntaxError: Non-hex character in Unicode escape sequence: {}){}