[korowai/ldaplib] Add errorHandler attribute to LdapLinkInterface

[ptomulik]

This way we avoid new LdapLinkErrorHandler($link) in lot of places.

[ptomulik]

This can also become a part of LdapLinkWrapperInterface.

[ptomulik]

Problem one: if $link is a mock for LdapLinkInterface then it needs getErrorHandler() method to be mocked everywhere. Quite unexpected.

[ptomulik]

It seems it simply would break SRP (Single Responsibility Principle). A side effect is that tests become more complicated.

[ptomulik]

Ok, let's make ErrorHandlerWrapperInterface as follows (perhaps in korowai/errorlib-interfaces)

interface ErrorHandlerWrapperInterface {
  public function getErrorHandler() : ErrorHandlerInterface;
}

and then

interface LdapLinkInterface extends ErrorHandlerWrapperInterface { /* ... */ }
interface LdapLinkWrapperInterface extends ErrorHandlerWrapperInterface { /* ... */ }

[ptomulik]

Done with LdapLinkInterface. Now let's do the same with LdapLinkWrapperInterface.