fix(terminal): report terminal window size in pixels

Window size in pixels is required by some programs, reporting it can
help those programs work inside NeoVim terminals.

See also: neovim#8259, neovim#12991

src/nvim/os/pty_process_unix.c

@@ -171,7 +171,13 @@ int pty_process_spawn(PtyProcess *ptyproc)
   Process *proc = (Process *)ptyproc;
   assert(proc->err.closed);
   uv_signal_start(&proc->loop->children_watcher, chld_handler, SIGCHLD);
-  ptyproc->winsize = (struct winsize){ ptyproc->height, ptyproc->width, 0, 0 };
+  ioctl(1, TIOCGWINSZ, &ptyproc->winsize);
+  ptyproc->winsize = (struct winsize){
+    ptyproc->height,
+    ptyproc->width,
+    ptyproc->winsize.ws_xpixel / ptyproc->winsize.ws_col * ptyproc->width,
+    ptyproc->winsize.ws_ypixel / ptyproc->winsize.ws_row * ptyproc->height,
+  };
   uv_disable_stdio_inheritance();
   int master;
   int pid = forkpty(&master, NULL, &termios_default, &ptyproc->winsize);
@@ -232,7 +238,13 @@ const char *pty_process_tty_name(PtyProcess *ptyproc)
 void pty_process_resize(PtyProcess *ptyproc, uint16_t width, uint16_t height)
   FUNC_ATTR_NONNULL_ALL
 {
-  ptyproc->winsize = (struct winsize){ height, width, 0, 0 };
+  ioctl(ptyproc->tty_fd, TIOCGWINSZ, &ptyproc->winsize);
+  ptyproc->winsize = (struct winsize){
+    height,
+    width,
+    ptyproc->winsize.ws_xpixel / ptyproc->winsize.ws_col * width,
+    ptyproc->winsize.ws_ypixel / ptyproc->winsize.ws_row * height,
+  };
   ioctl(ptyproc->tty_fd, TIOCSWINSZ, &ptyproc->winsize);
 }