fix: avoid node-based sdk-utils in default export for package

[djones]

@percy/agent is sometimes imported like this in our SDKs:

import PercyAgent from '@percy/agent'

At which point the default export is imported. This export is intended to run in a browser and everything in the src/percy-agent-client directory is built to expect this.

As we've built out our SDKs we found that @percy/agent is also quite useful for centralizing SDK utility functions. We previously had been distributing these util functions through the default export, so you can go:

import { agentJsFilename, isAgentRunning, postSnapshot } from '@percy/agent'

The problem with that is the util code would import other libraries, such as Winston, which are entirely designed to run on Node and not in a browser.

This PR simply removes the node-specific code from our default export, but as a result we've had to update our SDKs to reach inside @percy/agent and require these utils instead.

Those PRs are here:

• fix: require agentJsFilename directly from @percy/agent percy-protractor#36
• fix: require the SDK utils directly percy-webdriverio#73
• fix: require the SDK utils directly percy-nightwatch#38
• fix: require the SDK utils directly percy-puppeteer#75
• fix: require the SDK utils directly from @percy/agent percy-nightmare#53

Related issue:

• Error with Winston library percy-cypress#58

[Robdel12]

Very very excited about this! 🏁🏁