ProcessManager: Add a new per-proces "open files" view showing open FDs

This uses the data from /proc/PID/fds with ease now that it's JSON. :^)

Applications/ProcessManager/ProcessFileDescriptorMapWidget.h

@@ -0,0 +1,18 @@
+#pragma once
+
+#include <LibGUI/GWidget.h>
+
+class GTableView;
+
+class ProcessFileDescriptorMapWidget final : public GWidget {
+    C_OBJECT(ProcessFileDescriptorMapWidget);
+public:
+    explicit ProcessFileDescriptorMapWidget(GWidget* parent);
+    virtual ~ProcessFileDescriptorMapWidget() override;
+
+    void set_pid(pid_t);
+
+private:
+    GTableView* m_table_view { nullptr };
+    pid_t m_pid { -1 };
+};