Kernel+SystemMonitor: Expose amount of per-process dirty private memory

Dirty private memory is all memory in non-inode-backed mappings that's
process-private, meaning it's not shared with any other process.

This patch exposes that number via SystemMonitor, giving us an idea of
how much memory each process is responsible for all on its own.

Kernel/Process.cpp

@@ -2502,6 +2502,16 @@ void Process::die()
     }
 }
 
+size_t Process::amount_dirty_private() const
+{
+    size_t amount = 0;
+    for (auto& region : m_regions) {
+        if (!region.is_shared())
+            amount += region.amount_dirty();
+    }
+    return amount;
+}
+
 size_t Process::amount_virtual() const
 {
     size_t amount = 0;