tqdm.std: add update_to

Porting from dvc's Tqdm progress bar implementation.

https://github.com/iterative/dvc/blob/cf8195c829aa67425b87e4145bd33cae8584ee1e/dvc/progress.py#L114-L117

So, the implementation uses `self.update()` so that it refreshes based on `self.update()` logic.
Also, adds a way to update `total`.

This function is pretty convenient and useful even outside dvc. Take an example of fsspec's callback
that uses both `total` and `value` (i.e. current position) at once.

https://github.com/fsspec/filesystem_spec/blob/0ffe06cb767456b7c13904b57ec1c3ca60d53eae/fsspec/callbacks.py#L228

I see that there are mentions of `update_to` in docs and examples, which will likely have to change
as a result of this PR. So I'm happy to rename this to something else (eg: `set_position` etc.).

Related: #1264.

tqdm/cli.py

@@ -288,7 +288,7 @@ def callback(i):
                             t.update(numeric(i.decode()))
                     else:  # update_to
                         def callback(i):
-                            t.update(numeric(i.decode()) - t.n)
+                            t.update_to(numeric(i.decode()))
                     for i in stdin:
                         write(i)
                         callback(i)
@@ -304,7 +304,7 @@ def callback(i):
                         t.update(numeric(i.decode()))
                 elif update_to:
                     def callback(i):
-                        t.update(numeric(i.decode()) - t.n)
+                        t.update_to(numeric(i.decode()))
                 else:
                     callback = t.update
                     callback_len = True

tqdm/std.py

@@ -1263,6 +1263,11 @@ def update(self, n=1):
                 self.last_print_t = cur_t
                 return True
 
+    def update_to(self, n, total=None):
+        if total is not None:
+            self.total = total
+        self.update(n - self.n)
+
     def close(self):
         """Cleanup and (if leave=False) close the progressbar."""
         if self.disable: