Kernel: Rename Process::is_ring0/3 to Process::is_kernel/user_process

Since "rings" typically refer to code execution and user processes
can also execute in ring 0, rename these functions to more accurately
describe what they mean: kernel processes and user processes.

Kernel/FileSystem/ProcFS.cpp

@@ -830,7 +830,7 @@ static Optional<KBuffer> procfs$all(InodeIdentifier)
     auto build_process = [&](const Process& process) {
         auto process_object = array.add_object();
 
-        if (process.is_ring3()) {
+        if (process.is_user_process()) {
             StringBuilder pledge_builder;
 
 #define __ENUMERATE_PLEDGE_PROMISE(promise)      \