[WIP] Add externalInput function

[levimatheri]

Adds new externalInput function under experimental feature flag.

Microsoft Reviewers: Open in CodeFlow

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 9.37%. Comparing base (108d816) to head (e85e8b3).
Report is 2191 commits behind head on main.

❗ There is a different number of reports uploaded between BASE (108d816) and HEAD (e85e8b3). Click for more details.

HEAD has 4 uploads less than BASE

Flag	BASE (108d816)	HEAD (e85e8b3)
dotnet	4	0

Additional details and impacted files

@@             Coverage Diff             @@
##             main   #16682       +/-   ##
===========================================
- Coverage   94.28%    9.37%   -84.91%     
===========================================
  Files        1113        7     -1106     
  Lines      100791      288   -100503     
  Branches     8734      121     -8613     
===========================================
- Hits        95028       27    -95001     
+ Misses       4595      261     -4334     
+ Partials     1168        0     -1168     

Flag	Coverage Δ
dotnet	?
typescript	9.37% <ø> (+1.66%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

see 1102 files with indirect coverage changes

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.