Implement multi-window drag-and-drop under Android

* java/org/gnu/emacs/EmacsNative.java (sendDndDrag, sendDndUri)
(sendDndText): Declare new event-sending functions.

* java/org/gnu/emacs/EmacsView.java (onDragEvent): New function.

* java/org/gnu/emacs/EmacsWindow.java (onDragEvent): New
function; respond to each drag and drop event, request
permissions if necessary and transfer dropped data to Lisp.

* lisp/dnd.el (dnd-unescape-file-uris): New variable.
(dnd-get-local-file-name): If that variable is nil, refrain from
unescaping URLs provided.

* lisp/term/android-win.el (android-handle-dnd-event): New
function.
(special-event-map): Bind drag-n-drop-event.

* src/android.c (sendDndDrag, sendDndUri, sendDndText): New
functions.

* src/androidgui.h (enum android_event_type): New event types
ANDROID_DND_DRAG_EVENT, ANDROID_DND_URI_EVENT,
ANDROID_DND_TEXT_EVENT.
(struct android_dnd_event): New structure.
(union android_event) <dnd>: New field.

* src/androidterm.c (handle_one_android_event)
<ANDROID_DND_..._EVENT>: Generate drag-n-drop events for each
of these types.
(syms_of_androidterm) <Quri, Qtext>: New defsyms.

1 files changed, 30 insertions, 0 deletions

diff --git a/src/androidgui.h b/src/androidgui.h
index b58c39a5276..5fab5023ba4 100644
--- a/src/androidgui.h
+++ b/src/androidgui.h
@@ -248,6 +248,9 @@ enum android_event_type
     ANDROID_CONTEXT_MENU,
     ANDROID_EXPOSE,
     ANDROID_INPUT_METHOD,
+    ANDROID_DND_DRAG_EVENT,
+    ANDROID_DND_URI_EVENT,
+    ANDROID_DND_TEXT_EVENT,
   };
 
 struct android_any_event
@@ -510,6 +513,28 @@ struct android_ime_event
   unsigned long counter;
 };
 
+struct android_dnd_event
+{
+  /* Type of the event.  */
+  enum android_event_type type;
+
+  /* The event serial.  */
+  unsigned long serial;
+
+  /* The window that gave rise to the event.  */
+  android_window window;
+
+  /* X and Y coordinates of the event.  */
+  int x, y;
+
+  /* Data tied to this event, such as a URI or clipboard string.
+     Must be deallocated with `free'.  */
+  unsigned short *uri_or_string;
+
+  /* Length of that data.  */
+  size_t length;
+};
+
 union android_event
 {
   enum android_event_type type;
@@ -541,6 +566,11 @@ union android_event
 
   /* This is used to dispatch input method editing requests.  */
   struct android_ime_event ime;
+
+  /* There is no analog under X because Android defines a strict DND
+     protocol, whereas there exist several competing X protocols
+     implemented in terms of X client messages.  */
+  struct android_dnd_event dnd;
 };
 
 enum