MDL-73352 phpunit: lib_test and locallib_test testcase names
All lib_test and locallib_test classes: - Namespaced with component (and API whenever makes sense). - Fixed incorrect use statements with leading backslash. - Changed code to point to global scope when needed or add new uses. - All them passing individually. - Complete runs passing too. Special mention to tests under login/tests: 1) The core_login component doesn't exist. 2) But login/tests are allowed because there is a suite pointing to it (phpunit.xml). 3) So, the only possible namespace for them is "core". 4) And to avoid problems with other core testcases (under lib/tests) they have been renamed to have login_xxxx as prefix.