Pnpjs: [2.0.0] sub module: SP-folders

[PopWarner]

This issue tracks the review and preparation of a sub module for the 2.0.0 project. To finalize a sub-module the follow steps should be performed:

• [ ] Code review for TODO (do), commented out code (remove), ensure interfaces are prefixed with an "I", or not using await
• [ ] Ensure every property/method has at least one test
• [ ] Ensure all of the interface method/properties are commented
• [ ] Remove comments from class implementation files
• [ ] Ensure the docs page is updated to mention each method/property with at least a minimal example
• [ ] Search in closed issue by the label "area: sample" to see if any apply to the module you are review and add those as appropriate to the documentation
• [ ] Review/compare the code in the 1.x branch to ensure any fixes, updates, or changes are in 2.0

Once complete submit one PR per module for final review. Please make the title match the issue title and reference the issue in the body of the PR. It will then be reviewed so please check back for any feedback or questions.

[s-KaiNet]

Hey guys! @juliemturner @simonagren @PopWarner.
I would like to work on and complete the tasks for this submodule 👌😃

[PopWarner]

WOO WOO @s-KaiNet! :) Thanks my man. I've updated the label from "status: help wanted" to "status:in progress" and it's ready for ya! 👍