patch 8.2.3040: GUI: dropping files not tested

Problem:    GUI: dropping files not tested.
Solution:   Add test_gui_drop_files() and tests. (Yegappan Lakshmanan,
            closes #8434)

runtime/doc/eval.txt

@@ -3022,6 +3022,8 @@ test_feedinput({string})	none	add key sequence to input buffer
 test_garbagecollect_now()	none	free memory right now for testing
 test_garbagecollect_soon()	none	free memory soon for testing
 test_getvalue({string})		any	get value of an internal variable
+test_gui_drop_files({list}, {row}, {col}, {mods})
+				none	drop a list of files in a window
 test_gui_mouse_event({button}, {row}, {col}, {repeated}, {mods})
 				none	add a mouse event to the input buffer
 test_ignore_error({expr})	none	ignore a specific error

runtime/doc/testing.txt

@@ -79,10 +79,23 @@ test_getvalue({name})					*test_getvalue()*
 		Can also be used as a |method|: >
 			GetName()->test_getvalue()
 <
+						*test_gui_drop_files()*
+test_gui_drop_files({list}, {row}, {col}, {mods})
+		Drop one or more files in {list} in the window at {row}, {col}.
+		This function only works when the GUI is running.
+		
+		The supported values for {mods} are:
+			0x4	Shift
+			0x8	Alt
+			0x10	Ctrl
+		The files are added to the argument list and the first file in
+		{list} is edited in the window.  See |drag-n-drop| for more
+		information.
+
 						*test_gui_mouse_event()*
 test_gui_mouse_event({button}, {row}, {col}, {multiclick}, {modifiers})
-		Inject a mouse button click event.  This function works only
-		when GUI is running.
+		Inject a mouse button click event.  This function only works
+		when the GUI is running.
 		The supported values for {button} are:
 			0	right mouse button
 			1	middle mouse button
@@ -92,7 +105,9 @@ test_gui_mouse_event({button}, {row}, {col}, {multiclick}, {modifiers})
 			5	scroll wheel up
 			6	scroll wheel left
 			7	scroll wheel right
-		{row} and {col} specify the location of the mouse click.
+		{row} and {col} specify the location of the mouse click. The
+		first row of the Vim window is 1 and the last row is 'lines'.
+		The maximum value of {col} is 'columns'.
 		To inject a multiclick event, set {multiclick} to 1.
 		The supported values for {modifiers} are:
 			4	shift is pressed

runtime/doc/usr_41.txt

@@ -1021,6 +1021,7 @@ Testing:				    *test-functions*
 	test_garbagecollect_now()   free memory right now
 	test_garbagecollect_soon()  set a flag to free memory soon
 	test_getvalue()		get value of an internal variable
+	test_gui_drop_files()	drop file(s) in a window
 	test_gui_mouse_event()	add a GUI mouse event to the input buffer
 	test_ignore_error()	ignore a specific error message
 	test_null_blob()	return a null Blob