Fix for ignoring the result of scheme mapping

[TotenTraum]

When loading a schema that uses the "$schema" property set to "http://json-schema.org/schema#" that references the latest version of the specification, the following exception is thrown

java.io.FileNotFoundException: classpath:schema

Afterwards I decided to add mapping for such a case, but it still throws the same exception

final VersionFlag versionFlag = VersionFlag.V7;
final String schemaIri = JsonSchemaFactory.checkVersion(versionFlag).getInstance().getIri();

final JsonSchemaFactory jsonSchemaFactory = JsonSchemaFactory.getInstance(versionFlag, builder ->
     builder.schemaMappers(schemaMappers -> schemaMappers.mappings(Map.of("http://json-schema.org/schema", schemaIri)))
);

It turned out that the code of the DefaultSchemaLoader class ignores the mapping result

...
AbsoluteIri mappedResult = absoluteIri; <-----
for (SchemaMapper mapper : schemaMappers) {
    AbsoluteIri mapped = mapper.map(mappedResult);
    if (mapped != null) {
         mappedResult = mapped;
       }
    }
    AbsoluteIri mapped = META_SCHEMA_MAPPER.map(absoluteIri); <----
    if (mapped != null) {
        mappedResult = mapped;
    }
...

[justin-tay]

Just a note that the use of http://json-schema.org/schema# to refer to the latest version is deprecated and should not be used. See https://json-schema.org/understanding-json-schema/reference/schema. Dialects are not backward compatible so you may get unexpected results.

That said you need to add a unit test for the pull request for this to be reviewed if this is still something you want.