Factor out SigningTestCase for reuse

Supress warning on absent NameIDFormat

In https://github.com/simplesamlphp/simplesamlphp/pull/972 we moved the
phpunit config to the root of the project. This was not updated in the
testing documentation.

HHVM is not compatible with Symfony4 and it is no longer worth the hassle

Allows sharing a valid certificate setup with SignerTest. In SignerTest,
reuse good certificate as the main certificate for signature and add a
second certificate for testSignWithMultiCertificate.

Deprecation warning: require-dev.mikey179/vfsStream is invalid, it should not contain uppercase characters.

This is because of the positioning of the elements which triggers
a clipboard.js bug: zenorocha/clipboard.js#382
Removing the whitespace around the HTML tags works around this issue.

closes: #1041

It was split into MissingParamType and MissingClosureParamType

It was removed by Psalm in a future version, so will cause errors as soon as we upgrade

Was broken in fecd5cf6

Allow StandardErrorLoggingHandler to be used