LibCore: Implement a helper that waits for a debugger then breaks

This method can be used to force the current process to sleep, waiting
for a debugger to attach. On attach, the debugger breaks at the callsite
 directly.

This is tested on Linux and macOS, in Clion and also terminal gdb and
lldb.

Userland/Libraries/LibCore/Process.h

@@ -31,6 +31,7 @@ public:
     };
     static ErrorOr<void> set_name(StringView, SetThreadName = SetThreadName::No);
 
+    static void wait_for_debugger_and_break();
     static ErrorOr<bool> is_being_debugged();
 };