Refactor checkFetch from a separate method to a proxy around fetch

[evanderkoogh]

Fixes #3478

What this PR solves / how to test:

This PR makes it possible to locally test Workers where the global fetch object is proxied with a Javascript Proxy.
While this won't happen often in regular Workers, things like the Open Telemetry SDK do need that to intercept and instrument outgoing fetch calls.

Associated docs issue(s)/PR(s):

This does not change any externally observable behaviour, so no tests are needed.

Author has included the following, where applicable:

• Tests (NA, no outside observable behaviour change)
• Changeset (Changeset guidelines)

Reviewer is to perform the following, as applicable:

• Checked for inclusion of a relevant changeset
• Checked for creation of associated docs updates
• Manually pulled down the changes and spot-tested

[changeset-bot]

🦋 Changeset detected

Latest commit: f221a61

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
wrangler	Patch

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Click here if you're a maintainer who wants to add another changeset to this PR

[github-actions]

A wrangler prerelease is available for testing. You can install this latest build in your project with:

npm install --save-dev https://prerelease-registry.devprod.cloudflare.dev/workers-sdk/runs/5322410902/npm-package-wrangler-3497

You can reference the automatically updated head of this PR with:

npm install --save-dev https://prerelease-registry.devprod.cloudflare.dev/workers-sdk/prs/3497/npm-package-wrangler-3497

Or you can use npx with this latest build directly:

npx https://prerelease-registry.devprod.cloudflare.dev/workers-sdk/runs/5322410902/npm-package-wrangler-3497 dev path/to/script.js

Additional artifacts:

npm install https://prerelease-registry.devprod.cloudflare.dev/workers-sdk/runs/5322410902/npm-package-cloudflare-pages-shared-3497

Note that these links will no longer work once the GitHub Actions artifact expires.

[codecov]

Codecov Report

Merging #3497 (f221a61) into main (9fd12df) will increase coverage by 0.02%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##             main    #3497      +/-   ##
==========================================
+ Coverage   75.18%   75.21%   +0.02%     
==========================================
  Files         183      183              
  Lines       11055    11054       -1     
  Branches     2904     2903       -1     
==========================================
+ Hits         8312     8314       +2     
+ Misses       2743     2740       -3     

Impacted Files	Coverage Δ
packages/wrangler/src/bundle.ts	93.82% <ø> (-0.04%)	⬇️

... and 2 files with indirect coverage changes

[petebacondarwin]

Nice little feature @evanderkoogh.
I have pulled this down and tried it out locally. It appears to work as expected.
(@evanderkoogh - I note your GH profile still says you are a PM at Cloudflare!)