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/FieldAliasMapperValidationTests.java
}
    public void testAliasWithNonExistentPath() {
        FieldAliasMapper invalidAlias = new FieldAliasMapper("invalid-alias", "invalid-alias", "non-existent");
        MapperParsingException e = expectThrows(MapperParsingException.class, () -> {
            MappingLookup mappers = createMappingLookup(emptyList(), emptyList(), singletonList(invalidAlias), emptyList());
            invalidAlias.validate(mappers);
        });
        assertEquals(
            "Invalid [path] value [non-existent] for field alias [invalid-alias]: an alias"
                + " must refer to an existing field in the mappings.",
            e.getMessage()
        );
    }
    public void testFieldAliasWithNestedScope() {
        ObjectMapper objectMapper = createNestedObjectMapper("nested");
        FieldAliasMapper aliasMapper = new FieldAliasMapper("alias", "nested.alias", "nested.field");
        MappingLookup mappers = createMappingLookup(
            singletonList(createFieldMapper("nested", "field")),
            singletonList(objectMapper),
            singletonList(aliasMapper),
            emptyList()
        );
        aliasMapper.validate(mappers);
    }
    public void testFieldAliasWithDifferentObjectScopes() {
        FieldAliasMapper aliasMapper = new FieldAliasMapper("alias", "object2.alias", "object1.field");
        MappingLookup mappers = createMappingLookup(
            List.of(createFieldMapper("object1", "field")),
            List.of(createObjectMapper("object1"), createObjectMapper("object2")),
            singletonList(aliasMapper),