Kernel: Annotate all syscalls with VERIFY_PROCESS_BIG_LOCK_ACQUIRED

Before we start disabling acquisition of the big process lock for
specific syscalls, make sure to document and assert that all the
lock is held during all syscalls.

Kernel/Syscalls/anon_create.cpp

@@ -13,6 +13,7 @@ namespace Kernel {
 
 KResultOr<FlatPtr> Process::sys$anon_create(size_t size, int options)
 {
+    VERIFY_PROCESS_BIG_LOCK_ACQUIRED(this);
     REQUIRE_PROMISE(stdio);
 
     if (!size)