Make Shift-PgUp and Shift-PgDn scroll by pages rather than lines

In other terminals, such as gnome-terminal, Shift-PgUp and Shift-PgDn
scroll the screen by a full page, rather than a single line. Adjust
termux to match.

terminal-view/src/main/java/com/termux/view/TerminalView.java

@@ -894,7 +894,7 @@ public boolean handleKeyCodeAction(int keyCode, int keyMod) {
                 if (shiftDown) {
                     long time = SystemClock.uptimeMillis();
                     MotionEvent motionEvent = MotionEvent.obtain(time, time, MotionEvent.ACTION_DOWN, 0, 0, 0);
-                    doScroll(motionEvent, keyCode == KeyEvent.KEYCODE_PAGE_UP ? -1 : 1);
+                    doScroll(motionEvent, keyCode == KeyEvent.KEYCODE_PAGE_UP ? -mEmulator.mRows : mEmulator.mRows);
                     motionEvent.recycle();
                     return true;
                 }