[Draft] Re-written inquirer package with new prompts

[SBoudrias]

WIP rewriting the core features of the main inquirer package on top of the new prompt system.

Goal is removing run-async and rxjs to ship a smaller/simpler package. But keep the rest backward compatible as much as possible.

Current problem:

• Typescript makes it hard to get strict typings; e.g. add confirm prompt in and it'll start failing.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 81.49%. Comparing base (0dfa6bd) to head (8fe03bc).
Report is 7 commits behind head on master.

❗ Current head 8fe03bc differs from pull request most recent head 1e1e40d. Consider uploading reports for the commit 1e1e40d to get more accurate results

Additional details and impacted files

@@             Coverage Diff             @@
##           master    #1173       +/-   ##
===========================================
- Coverage   94.46%   81.49%   -12.98%     
===========================================
  Files          53       39       -14     
  Lines        4556     4663      +107     
  Branches      772      677       -95     
===========================================
- Hits         4304     3800      -504     
+ Misses        247      193       -54     
- Partials        5      670      +665     

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