Autopopulate arduino.path with arduino-cli when a package manager is used

[austinoneil]

• Check for arduino-cli installation
• Refactor platforms to use factory function, interface to enforce consistency
• Refactor parts to have platform injected for easier testing

[fearthecowboy]

@austinoneil - this PR has conflicts -- can you resolve those and update the PR ?

[lersi]

hello, I created a community fork at https://github.com/vscode-arduino/vscode-arduino.
You are more than welcome to merge your changes there.