wpt: add FormData wpts

[KhafraDev]

Fixes 2 issues in FormData:

• new FormData(null) should throw
• have File entries inherit the lastModified property

These tests only take ~330 ms to run.

[codecov-commenter]

Codecov Report

Base: 89.55% // Head: 89.53% // Decreases project coverage by -0.01% ⚠️

Coverage data is based on head (71fabcf) compared to base (3f9d694).
Patch coverage: 100.00% of modified lines in pull request are covered.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1722      +/-   ##
==========================================
- Coverage   89.55%   89.53%   -0.02%     
==========================================
  Files          58       58              
  Lines        5257     5258       +1     
==========================================
  Hits         4708     4708              
- Misses        549      550       +1     

Impacted Files	Coverage Δ
lib/fetch/formdata.js	96.00% <100.00%> (+0.04%)	⬆️
lib/fetch/file.js	90.00% <0.00%> (-1.00%)	⬇️

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[mcollina]

lgtm