fix(fetch): allow custom implementation of AbortSignal

[SukkaW]

The PR closes #1605.

A test case is added to ensure it is the DOMException being thrown, not TypeError.

cc @mcollina @KhafraDev

[codecov-commenter]

Codecov Report

Merging #1608 (dd0bd7e) into main (5890e16) will decrease coverage by 0.02%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##             main    #1608      +/-   ##
==========================================
- Coverage   94.90%   94.88%   -0.03%     
==========================================
  Files          50       50              
  Lines        4753     4752       -1     
==========================================
- Hits         4511     4509       -2     
- Misses        242      243       +1     

Impacted Files	Coverage Δ
lib/fetch/request.js	85.06% <ø> (+0.35%)	⬆️
lib/fetch/file.js	91.66% <0.00%> (-1.20%)	⬇️
lib/fetch/webidl.js	97.74% <0.00%> (-0.57%)	⬇️

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[KhafraDev]

This wasn't the correct solution; it makes us fall out of line with the spec. Instead, when parsing an AbortSignal, a strict option should have been passed instead. See

undici/lib/fetch/webidl.js

Line 282 in e46d8bf

if (opts.strict !== false && !(V instanceof i)) {

Of course the webidl interface converter could also be improved such that when passing a strict: false option, it would check the object's Symbol.toStringTag/constructor name.