refactor(iec): Rename 'Invoke-ExternalCommand()' to 'Start-ExternalProcess()' and support EnvVars/WorkingDirectory

[niheaven]

Description

• Rename Invoke-ExternalCommand() to Start-ExternalProcess()
• Add environment variables and working directory suport

Motivation and Context

• Rename Activity to Prompt
• Rename LogPath to LogName
• Always redirect standard output and error, otherwise the function will not print its output to screen even if LogName is not set (related to #5066)
• Allow environment variables be set (related to #5122)
• Allow working directory be set (related to #5122)

How Has This Been Tested?

With proxy server on and off.

For the strange git ls-remotes output: git print From https://github.com/ScoopInstaller/Tests via the error output 🤣

Checklist:

• [x] I have read the Contributing Guide.
• [x] I have ensured that I am targeting the develop branch.
• [ ] I have updated the documentation accordingly.
• [ ] I have updated the tests accordingly.
• [ ] I have added an entry in the CHANGELOG.