Kernel+SystemMonitor: Publish can_read/write state for open files

The can_read() and can_write() states for file descriptions are now
published in /proc, allowing SystemMonitor to display it.

Applications/SystemMonitor/ProcessFileDescriptorMapWidget.cpp

@@ -25,6 +25,12 @@ ProcessFileDescriptorMapWidget::ProcessFileDescriptorMapWidget(GWidget* parent)
     pid_fds_fields.empend("On exec", TextAlignment::CenterLeft, [](auto& object) {
         return object.get("cloexec").to_bool() ? "Close" : "Keep";
     });
+    pid_fds_fields.empend("Can read", TextAlignment::CenterLeft, [](auto& object) {
+        return object.get("can_read").to_bool() ? "Yes" : "No";
+    });
+    pid_fds_fields.empend("Can write", TextAlignment::CenterLeft, [](auto& object) {
+        return object.get("can_write").to_bool() ? "Yes" : "No";
+    });
 
     m_table_view->set_model(GJsonArrayModel::create({}, move(pid_fds_fields)));
 }

Kernel/FileSystem/ProcFS.cpp

@@ -226,6 +226,8 @@ Optional<KBuffer> procfs$pid_fds(InodeIdentifier identifier)
         description_object.add("offset", description->offset());
         description_object.add("cloexec", cloexec);
         description_object.add("blocking", description->is_blocking());
+        description_object.add("can_read", description->can_read());
+        description_object.add("can_write", description->can_write());
     }
     array.finish();
     return builder.build();

Kernel/Net/LocalSocket.cpp

@@ -195,7 +195,7 @@ bool LocalSocket::can_read(const FileDescription& description) const
         return !has_attached_peer(description) || !m_for_server.is_empty();
     if (role == Role::Connected)
         return !has_attached_peer(description) || !m_for_client.is_empty();
-    ASSERT_NOT_REACHED();
+    return false;
 }
 
 bool LocalSocket::has_attached_peer(const FileDescription& description) const
@@ -215,7 +215,7 @@ bool LocalSocket::can_write(const FileDescription& description) const
         return !has_attached_peer(description) || m_for_client.bytes_in_write_buffer() < 16384;
     if (role == Role::Connected)
         return !has_attached_peer(description) || m_for_server.bytes_in_write_buffer() < 16384;
-    ASSERT_NOT_REACHED();
+    return false;
 }
 
 ssize_t LocalSocket::sendto(FileDescription& description, const void* data, size_t data_size, int, const sockaddr*, socklen_t)