feat(tui): recognize X1 and X2 mouse events

Ref:
https://invisible-island.net/xterm/ctlseqs/ctlseqs.html#h3-Other-buttons

Author: zeertzjq

src/nvim/os/input.c

@@ -403,6 +403,7 @@ static unsigned handle_mouse_event(const char **ptr, uint8_t *buf, unsigned bufs
 
   if (type != KS_EXTRA
       || !((mouse_code >= KE_LEFTMOUSE && mouse_code <= KE_RIGHTRELEASE)
+           || (mouse_code >= KE_X1MOUSE && mouse_code <= KE_X2RELEASE)
            || (mouse_code >= KE_MOUSEDOWN && mouse_code <= KE_MOUSERIGHT)
            || mouse_code == KE_MOUSEMOVE)) {
     return bufsize;

src/nvim/tui/input.c

@@ -387,6 +387,10 @@ static void forward_mouse_event(TermInput *input, TermKeyKey *key)
     len += (size_t)snprintf(buf + len, sizeof(buf) - len, "Middle");
   } else if (button == 3) {
     len += (size_t)snprintf(buf + len, sizeof(buf) - len, "Right");
+  } else if (button == 8) {
+    len += (size_t)snprintf(buf + len, sizeof(buf) - len, "X1");
+  } else if (button == 9) {
+    len += (size_t)snprintf(buf + len, sizeof(buf) - len, "X2");
   }
 
   switch (ev) {

src/nvim/tui/termkey/driver-csi.c

@@ -327,6 +327,12 @@ TermKeyResult termkey_interpret_mouse(TermKey *tk, const TermKeyKey *key, TermKe
     btn = code + 4 - 64;
     break;
 
+  case 128:
+  case 129:
+    *event = drag ? TERMKEY_MOUSE_DRAG : TERMKEY_MOUSE_PRESS;
+    btn = code + 8 - 128;
+    break;
+
   default:
     *event = TERMKEY_MOUSE_UNKNOWN;
   }