Add spec for adding commandline arguments to wt.exe (#3495)

## Summary of the Pull Request

This is the spec for adding commandline arguments to the Windows Terminal. This includes design work for a powerful future version of the commandline args for the Terminal, as well as a way that system could be implemented during 1.0 to provide basic functionality, while creating commandlines that will work without modification in (a future Windows Terminal version).   

## References

Referenced in the course of this spec:

* #607  Feature Request: wt.exe supports command line arguments (profile, command, directory, etc.) 
* #1060 Add "open Windows terminal here" into right-click context menu 
* #576  Feature Request: Task Bar jumplist should show items from profile 
* #1357 Draft spec for adding profiles to the Windows jumplist 
* #2080 Spec for tab tear off and default app 
* #632  [Question] Configuring Windows Terminal profile to always launch elevated 
* #2068 New window key binding not working 

## PR Checklist
* [x] Specs #607
* [x] I work here
* [x] _it's a spec_

## Detailed Description of the Pull Request / Additional comments

Read the spec.

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* Let's commit this bewfore I go hog-wild on new-window

* new-window vs new-tab discussion

* Well, this is ready for a review

* -P -> -% for --percent

* Big note on powershell

  of course, powershell has to use `;` as the command seperator

* Minor typos

* This is a lot of feedback from PR

  bigly, it's focus-pane and focus-tab

* Add notes on implementation, based on investigation

* Apply suggestions from @miniksa

* some updates after actually implementing the thing

* some minor things from PR

* Apply suggestions from code review

Co-Authored-By: Dustin L. Howett (MSFT) <[email protected]>

* comments from dustin's latest review

* more comments from dustin

* mostly just typos

Co-authored-by: Dustin L. Howett (MSFT) <[email protected]>