### Elasticsearch Version

main

### Installed Plugins

_No response_

### Java Version

_bundled_

### OS Version

all

### Problem Description

When you configure an `aggregate_metric_double` with `ignore_malformed: true` and send a malformed value we create an `_ignored` field with three values, `field.value_count`, `field.min`, and `field.max`. This is the only top "composite" field that creates `_ignored` values for its children. Things like shape only create `field` in `_ignored`. Is there a good reason for `aggregate_metric_double` to be different?

### Steps to Reproduce

see above

### Logs (if relevant)

_No response_
x-pack/plugin/mapper-aggregate-metric/src/test/java/org/elasticsearch/xpack/aggregatemetric/mapper/AggregateDoubleMetricFieldMapperTests.java
minimalMapping(b);
                b.field("time_series_metric", "counter");
            })));
            assertThat(
                e.getCause().getMessage(),
                containsString("Unknown value [counter] for field [time_series_metric] - accepted values are [gauge]")
            );
        }
        {
            
            Exception e = expectThrows(MapperParsingException.class, () -> createMapperService(fieldMapping(b -> {
                minimalMapping(b);
                b.field("time_series_metric", "unknown");
            })));
            assertThat(
                e.getCause().getMessage(),
                containsString("Unknown value [unknown] for field [time_series_metric] - accepted values are [gauge]")
            );
        }
    }
    @Override
    protected SyntheticSourceSupport syntheticSourceSupport(boolean ignoreMalformed) {
        assumeFalse("synthetic _source support for aggregate_double_metric doesn't support ignore_malformed", ignoreMalformed);
        return new AggregateDoubleMetricSyntheticSourceSupport();
    }
    @Override
    protected IngestScriptSupport ingestScriptSupport() {
        throw new AssumptionViolatedException("not supported");
    }
    protected final class AggregateDoubleMetricSyntheticSourceSupport implements SyntheticSourceSupport {