Implement flushing in Windows VT100 input (#2001)

Author: NewDefectus

src/prompt_toolkit/input/win32.py

@@ -104,8 +104,11 @@ def detach(self) -> ContextManager[None]:
     def read_keys(self) -> list[KeyPress]:
         return list(self.console_input_reader.read())
 
-    def flush(self) -> None:
-        pass
+    def flush_keys(self) -> None:
+        if self._use_virtual_terminal_input:
+            return self.console_input_reader.flush_keys()
+        else:
+            return []
 
     @property
     def closed(self) -> bool:
@@ -640,6 +643,20 @@ def read(self) -> Iterable[KeyPress]:
         self._buffer = []
         return result
 
+    def flush_keys(self) -> list[KeyPress]:
+        """
+        Flush pending keys and return them.
+        (Used for flushing the 'escape' key.)
+        """
+        # Flush all pending keys. (This is most important to flush the vt100
+        # 'Escape' key early when nothing else follows.)
+        self._vt100_parser.flush()
+
+        # Return result.
+        result = self._buffer
+        self._buffer = []
+        return result
+
     def _get_keys(
         self, read: DWORD, input_records: Array[INPUT_RECORD]
     ) -> Iterator[str]: