feat: add score attribute for image element

[KazuCocoa]

appium/appium#13883

Depends on appium/appium-support#169

After this change, we can get score image attribute like below:

• client (Ruby)

image_element =  @@driver.find_element_by_image AppiumLibCoreTest.path_of('test/functional/data/test_ios_button.png')
=> #<Selenium::WebDriver::Element:0x4de9c1e10ffa87de id="appium-image-element-e3b9dd5b-0c26-47a7-838a-6d72d61f62e7">
> image_element.score
=> 0.9313163161277771

• server

[HTTP] --> GET /wd/hub/session/97e811cd-d675-4f2c-a00e-ec79f5b1631b/element/appium-image-element-e3b9dd5b-0c26-47a7-838a-6d72d61f62e7/attribute/score
[HTTP] {}
[debug] [W3C (97e811cd)] Calling AppiumDriver.getAttribute() with args: ["score","appium-image-element-e3b9dd5b-0c26-47a7-838a-6d72d61f62e7","97e811cd-d675-4f2c-a00e-ec79f5b1631b"]
[debug] [XCUITest] Executing command 'getAttribute'
[debug] [W3C (97e811cd)] Responding to client with driver.getAttribute() result: 0.9313163161277771
[HTTP] <-- GET /wd/hub/session/97e811cd-d675-4f2c-a00e-ec79f5b1631b/element/appium-image-element-e3b9dd5b-0c26-47a7-838a-6d72d61f62e7/attribute/score 200 1 ms - 28
[HTTP]
[BaseDriver] Shutting down because we waited 120 seconds for a command
[Appium] Closing session, cause was 'New Command Timeout of 120 seconds expired. Try customizing the timeout using the 'newCommandTimeout' desired capability'
[Appium] Removing session '97e811cd-d675-4f2c-a00e-ec79f5b1631b' from our master session list
[DevCon Factory] Releasing connections for F9F30814-75E5-45DD-98A5-5650B97E63D2 device on any port number
[DevCon Factory] Found cached connections to release: ["F9F30814-75E5-45DD-98A5-5650B97E63D2:8100"]
[debug] [DevCon Factory] Cached connections count: 0
[debug] [XCUITest] Not clearing log files. Use `clearSystemFiles` capability to turn on.
[debug] [IOSSimulatorLog] Stopping iOS log capture