Refactor the way WebAssertTest performs assertions

Passing a callable instead of a method name and a list of arguments make
the test code statically analyzable and more clear.

Author: stof

phpstan-baseline.neon

@@ -39,8 +39,3 @@ parameters:
 message:"#^Parameter \\#2 \\$callback of method Behat\\\\Mink\\\\Element\\\\Element\\:\\:waitFor\\(\\) expects callable\\(\\)\\: mixed, 'not a callable' given\\.$#"
 count:1
 path:tests/Element/NodeElementTest.php
-
--
-message:"#^Parameter \\#1 \\$callback of function call_user_func_array expects callable\\(\\)\\: mixed, array\\{Behat\\\\Mink\\\\WebAssert, string\\} given\\.$#"
-count:2
-path:tests/WebAssertTest.php