Revert "chore: remove duplicated clean command" (appium#881)

* Revert "chore: remove duplicated clean command (appium#809)"

This reverts commit 2f45ef9.

* chore: left a comment

* trim spaces

Author: KazuCocoa

appium/webdriver/mobilecommand.py

@@ -31,6 +31,7 @@ class MobileCommand:
     DEACTIVATE_IME_ENGINE = 'deactivateIMEEngine'
     GET_ACTIVE_IME_ENGINE = 'getActiveEngine'
 
+    CLEAR = 'clear'
     LOCATION_IN_VIEW = 'locationInView'
 
     CONTEXTS = 'getContexts'

appium/webdriver/webdriver.py

@@ -575,6 +575,7 @@ def _add_commands(self) -> None:
             'POST',
             '/session/$sessionId/appium/element/$id/replace_value',
         )
+        commands[Command.CLEAR] = ('POST', '/session/$sessionId/element/$id/clear')
         commands[Command.LOCATION_IN_VIEW] = (
             'GET',
             '/session/$sessionId/element/$id/location_in_view',

appium/webdriver/webelement.py

@@ -144,6 +144,21 @@ def find_elements(self, by: str = AppiumBy.ID, value: Union[str, Dict, None] = N
 
         return self._execute(RemoteCommand.FIND_CHILD_ELEMENTS, {"using": by, "value": value})['value']
 
+    def clear(self) -> 'WebElement':
+        """Clears text.
+
+        Override for Appium
+
+        Returns:
+            `appium.webdriver.webelement.WebElement`
+        """
+
+        # NOTE: this method is overridden because the selenium client returned None instead of self.
+        # Appium python cleint would like to allow users to chain methods.
+        data = {'id': self.id}
+        self._execute(Command.CLEAR, data)
+        return self
+
     def set_text(self, keys: str = '') -> 'WebElement':
         """Sends text to the element.
         deprecated:: 2.8.1