[ChromeDriver] Add append behavior to file input with multiple property

Adding append behavior to send keys to input type=file with multiple property.
Also updating some error codes to match W3C specification.

When sending keys to input type=file multiple, previously chromedriver overwrote the files that already exist in the element.

It now appends as per W3C spec.
Additionally this change makes a small return code fix to match the W3C spec and adds an invalid argument error when empty string is sent to input type=file.

Bug: chromedriver:2721
Change-Id: Ibb009159d9d31f6d593a905ac00d3e215295aaad
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1510313
Reviewed-by: John Chen <johnchen@chromium.org>
Commit-Queue: Stanley Hon <stahon@microsoft.com>
Cr-Commit-Position: refs/heads/master@{#639119}
6 files changed