WELD-1751 Weld proxies fail access control checks when a SecurityManager...

... is present
It's faster to use Reflection.getCallerClass() (though you have to make some allowances for JDK bugs; see https://github.com/wildfly-security/security-manager/blob/master/src/main/java/org/wildfly/security/manager/WildFlySecurityManager.java#L107 and https://github.com/wildfly-security/security-manager/blob/master/src/main/java/org/wildfly/security/manager/WildFlySecurityManager.java#L128 for an example).