Enable compat with service workers and v3 extensions

[waltjones]

Description of the change

This PR adds a fetch transport for sending Rollbar payloads. This enables compatibility with Service Workers, and with manifest v3 extensions which now use a Service Worker for the background script.

The PR introduces a new optional config option, defaultTransport. When set to "fetch" or "xhr", this transport will be used when available. The default when not set is "xhr". When only one transport is detected to be available, that one will be used regardless of the defaultTransport setting.

Since we have two transports now, these are moved into a /transport/ subdir. This causes a large block diff in the PR for the existing xhr transport code. None of that code has been changed, just moved to a new file.

Type of change

• New feature (non-breaking change that adds functionality)

Related issues

• Fix [SC-118535]

#1040

Development

• Lint rules pass locally
• The code changed/added as part of this pull request has been covered with tests
• All tests related to the changed code pass in development

Code review

• This pull request has a descriptive title and information useful to a reviewer. There may be a screenshot or screencast attached
• "Ready for review" label attached to the PR and reviewers assigned
• Issue from task tracker has a link to this pull request
• Changes have been reviewed by at least one other engineer

[shortcut-integration]

This pull request has been linked to Shortcut Story #118535: Logging errors to rollbar from the service worker script within a chrome extension does not work..

[waltjones]

CI failure is fixed in this PR and will be resolved when it merges. #1055

[mudetroit]

This looks good, at some point we should probably start the migration over to fetch in general, though this creates some fun with node. For now though this looks like a pretty direct change