### Description

I was just looking at some Elasticsearch that had lots of "Improve "reloading search analyzers" logs coming from `MapperService` at the INFO level. In my particular case, it was being emitted because analyzers are reloaded as part of doing a recovery. This log is not really helpful as-is, I think we need to do the following:
 - Switch the level to DEBUG, it's not important enough to warrant an INFO log.
 - Add which index reloaded its search analyzers to the log.

What do you think?
server/src/main/java/org/elasticsearch/index/mapper/MapperService.java
newMapping = incomingMapping;
        } else {
            newMapping = currentMapper.mapping().merge(incomingMapping, reason);
        }
        return newMapping;
    }
    private boolean assertSerialization(DocumentMapper mapper) {
        
        final CompressedXContent mappingSource = mapper.mappingSource();
        Mapping newMapping = parseMapping(mapper.type(), mappingSource);
        if (newMapping.toCompressedXContent().equals(mappingSource) == false) {
            throw new AssertionError(
                "Mapping serialization result is different from source. \n--> Source ["
                    + mappingSource
                    + "]\n--> Result ["
                    + newMapping.toCompressedXContent()
                    + "]"
            );
        }
        return true;
    }
    /**
     * Return the document mapper, or {@code null} if no mapping has been put yet
     * or no documents have been indexed in the current index yet (which triggers a dynamic mapping update)
     */
    public DocumentMapper documentMapper() {
        return mapper;
    }
    /**
     * Returns {@code true} if the given {@code mappingSource} includes a type