The `ignore_malformed` option is supported by a few of our field types, mainly numerics and dates, to still accept the document when such fields hold malformed values. See https://www.elastic.co/guide/en/elasticsearch/reference/current/ignore-malformed.html. Also `ignore_malformed` is an index level setting that gets applied to all field types that support it. 

The boolean field type does not support `ignore_malformed` but it should, so that if a boolean field cannot be parsed as a boolean, the document can still be accepted.


server/src/test/java/org/elasticsearch/index/mapper/BooleanFieldMapperTests.java
return (fieldName, params, searchLookup, onScriptError) -> ctx -> new BooleanFieldScript(
                    fieldName,
                    params,
                    searchLookup,
                    OnScriptError.FAIL,
                    ctx
                ) {
                    @Override
                    public void execute() {}
                };
            }
            @Override
            protected BooleanFieldScript.Factory nonEmptyFieldScript() {
                return (fieldName, params, searchLookup, onScriptError) -> ctx -> new BooleanFieldScript(
                    fieldName,
                    params,
                    searchLookup,
                    OnScriptError.FAIL,
                    ctx
                ) {
                    @Override
                    public void execute() {
                        emit(true);
                    }
                };
            }
        };
    }
}