Track patched XHR requests for network breadcrumbs

[yousif-bugsnag]

Goal

Fixes two issues with the current xhr monkey patch for network breadcrumbs:

• previously XMLHttpRequest.send was overridden on the instance in order to record the duration of the request. However this causes a potential incompatibility issue with other libraries that may be monkey patching XHR and calling this.send - as observed with msw, where both libraries call into each other causing an infinite loop.
• If an XHR instance is re-used (i.e. open is called more than once) event listeners from previous uses were not removed, resulting in duplicate breadcrumbs being logged.

Design

send is now overridden on the prototype rather than the instance, and WeakMaps are used to store metadata and event listeners associated with tracked XHR instances.

The open override now just adds the request instance to a weak map along with it's method and url. When send is called, the request metadata and any existing event listeners are retrieved - if there are previous event listeners for the request these are removed before new ones are added.

XHR is not monkey-patched (and XHR breadcrumbs are disabled) if WeakMap is not available - this affects IE<=10.

Testing

Updated unit tests and relied on existing e2e tests.

[github-actions]

@bugsnag/browser bundle size diff

	Minified	Minfied + Gzipped
Before	44.42 kB	13.55 kB
After	44.71 kB	13.63 kB
±	⚠️ +291 bytes	⚠️ +84 bytes

code coverage diff

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