@devtools: Enable file uploads by changing input elements' value

[nextlevelbeard]

Proposed changes

Enables files uploads though input elements of type file by changing their value with addValue/setValue commands. Fixes #5090 , thanks to @takeya0x86

Usage (same as webdriver protocol)

input.setValue("/Users/user/files/file.txt") // Single
input.setValue("/Users/user/files/file.txt\n/Users/user/files/file2.txt") //Multiple
// also for addValue

Types of changes

• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update

Checklist

• I have read the CONTRIBUTING doc
• I have added tests that prove my fix is effective or that my feature works
• I have added necessary documentation (if appropriate)
• I have added proper type definitions for new commands (if appropriate)

Further comments

Reviewers: @webdriverio/project-committers

[christian-bromann]

Can we add an actual e2e test using http://guinea-pig.webdriver.io/index.html? It has a simple file upload form.

[christian-bromann]

👍 awesome, thanks!