Implement device-to-computer clipboard copy

On Ctrl+C:
 - the client sends a GET_CLIPBOARD command to the device;
 - the device retrieve its current clipboard text and sends it in a
   GET_CLIPBOARD device event;
 - the client sets this text as the system clipboard text, so that it
   can be pasted in another application.

Fixes <https://github.com/Genymobile/scrcpy/issues/145>

server/src/main/java/com/genymobile/scrcpy/wrappers/ClipboardManager.java

@@ -0,0 +1,33 @@
+package com.genymobile.scrcpy.wrappers;
+
+import android.content.ClipData;
+import android.os.IInterface;
+
+import java.lang.reflect.InvocationTargetException;
+import java.lang.reflect.Method;
+
+public class ClipboardManager {
+    private final IInterface manager;
+    private final Method getPrimaryClipMethod;
+
+    public ClipboardManager(IInterface manager) {
+        this.manager = manager;
+        try {
+            getPrimaryClipMethod = manager.getClass().getMethod("getPrimaryClip", String.class);
+        } catch (NoSuchMethodException e) {
+            throw new AssertionError(e);
+        }
+    }
+
+    public CharSequence getText() {
+        try {
+            ClipData clipData = (ClipData) getPrimaryClipMethod.invoke(manager, "com.android.shell");
+            if (clipData == null || clipData.getItemCount() == 0) {
+                return null;
+            }
+            return clipData.getItemAt(0).getText();
+        } catch (InvocationTargetException | IllegalAccessException e) {
+            throw new AssertionError(e);
+        }
+    }
+}