Within the renamed classes in the previous commit, there were a
few incorrect namespace, this commit fixes all them to be
correct component[\api] ones.
Also fix a few incorrect leading backslashes in namespace/use
statements. And tests extending renamed tests.
These are the only cases 100% safe to apply the renaming of the
testcase class names to match the file names.
All other cases are not safe, because they are missing namespace
and may enter into name conflicts. Adding namespaces is not as
simple as imagined because it implies to, also, add a good number
of modifications to core. See the issue for more details.
