Check whether http://macedir.org/entity-category is set in the EntityAttributes
before using it as argument in in_array(). This prevents a "TypeError:
in_array() expects parameter 2 to be array, null given" error.

This situation happens when we do have EntityAttributes in the metadata but
none of type "http://macedir.org/entity-category". An example is an IdP
supporting https://refeds.org/category/research-and-scholarship, which would
have "http://macedir.org/entity-category-support" but not per se also
"http://macedir.org/entity-category".

This was previously the case. However, when we introduced the new way to configure NameIDPolicy by using arrays, the default for old-style string configurations changed so AllowCreate was then unset. When unset, the SAML standard sets its default to false, effectively creating interoperability issues when uses upgraded SimpleSAMLphp without changing the configuration.

This resolves #1230.

PSR-12 compliancy

The last version of psalm breaks with array_key_exists(), so we use isset() instead.

Cannot provide array_filter() output directly to empty() in conditional in PHP <= 5.4.

Take #2. Use the recently migrated SimpleSAML_Logger::maskErrors() and popErrorMask() methods to simplify code un SimpleSAML\Utils\Config\Metadata.

Use InvalidArgumentException instead of SimpleSAML_Error_Exception when dealing with wrong input parameters.

Deprecate SimpleSAML_Utilities::getDefaultEndpoint().

Extract constant information out of the getContact() function and make it public static properties of the class.