fix(instrumentation-fetch): fetch(string, Request) silently drops request body

[t2t2]

Which problem is this PR solving?

tl;dr: Fetch instrumentation drops request body when using Request object.

Currently fetch instrumentation forwards calls via 2 parameter signature regardless if 'fetch(Request)orfetch(url, object)` signature is being used:

opentelemetry-js/packages/opentelemetry-instrumentation-fetch/src/fetch.ts

Line 299 in 90ea0fe

const url = input instanceof Request ? input.url : input;

This however is causing a bug where passing request object as 2nd parameter drops request body: https://jsfiddle.net/t2t2/bc53reqf/

(confirmed with both Firefox 90.0.2 & Chrome 92.0.4515.131)

In quick research found that while Request.body should return a ReadableStream none of the browsers actually do it right now. fetch(url, object) is probably trying to find body from 2nd parameter as a normal object but isn't finding anything.

Short description of the changes

In case of fetch(Request) call original method with the same signature.

[codecov]

Codecov Report

Merging #2411 (a6250b4) into main (90ea0fe) will increase coverage by 0.49%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main    #2411      +/-   ##
==========================================
+ Coverage   92.14%   92.64%   +0.49%     
==========================================
  Files         120      137      +17     
  Lines        3998     4975     +977     
  Branches      844     1048     +204     
==========================================
+ Hits         3684     4609     +925     
- Misses        314      366      +52     

Impacted Files	Coverage Δ
...s/opentelemetry-instrumentation-fetch/src/fetch.ts	96.91% <100.00%> (ø)
.../opentelemetry-exporter-collector/src/transform.ts	88.69% <0.00%> (ø)
...ry-exporter-collector/src/CollectorExporterBase.ts	92.15% <0.00%> (ø)
packages/opentelemetry-sdk-trace-web/src/utils.ts	94.90% <0.00%> (ø)
...ry-context-zone-peer-dep/src/ZoneContextManager.ts	85.18% <0.00%> (ø)
...-sdk-trace-web/src/enums/PerformanceTimingNames.ts	100.00% <0.00%> (ø)
...ation-xml-http-request/src/enums/AttributeNames.ts	100.00% <0.00%> (ø)
...lemetry-exporter-collector/src/transformMetrics.ts	95.71% <0.00%> (ø)
...kages/opentelemetry-exporter-collector/src/util.ts	100.00% <0.00%> (ø)
...-instrumentation-fetch/src/enums/AttributeNames.ts	100.00% <0.00%> (ø)
... and 8 more