[lldb] Re-eanble and rewrite TestCPPStaticMembers

It's not clear why the whole test got disabled, but the linked bug report
has since been fixed and the only part of it that still fails is the test
for the too permissive lookup. This re-enables the test, rewrites it to use
the modern test functions we have and splits the failing part into its
own test that we can skip without disabling the rest.