* ♻ Refactor browser constructor to use percy instance reference

* ♻ Refactor core generator utils and usage

The generatePromise function now accepts an abort signal and node-style callback. Rather than
returning a promise-like generator, it now always returns a promise.

A new AbortController polyfill was added for Node environments to support providing the
generatorPromise function with an abort signal.

A yieldFor function replaces the previous waitFor function with the same basic functionality;
yielding on every iteration to the provided predicate function.

The waitFor function is now a shortcut for generatePromise(yieldFor(...args)).

A new waitForTimeout function was added in preperation of more exec utils.

* ♻ Use core generator and abort utils for cli-command

* ✨ Introduce additional core exec helpers

* 🚨 Remove empty comment

* ✅ Make some test variables constants

These are not reset during hooks, so they can leak between tests when redefined

* 🙈 Ignore coverage of injected code

Also adjusted two merge snapshot option paths that I noticed from logged empty arrays

Bumps [karma](https://github.com/karma-runner/karma) from 6.3.19 to 6.3.20.
- [Release notes](https://github.com/karma-runner/karma/releases)
- [Changelog](https://github.com/karma-runner/karma/blob/master/CHANGELOG.md)
- [Commits](karma-runner/karma@v6.3.19...v6.3.20)

---
updated-dependencies:
- dependency-name: karma
  dependency-type: direct:development
  update-type: version-update:semver-patch
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Bumps [yaml](https://github.com/eemeli/yaml) from 2.0.1 to 2.1.0.
- [Release notes](https://github.com/eemeli/yaml/releases)
- [Commits](eemeli/yaml@v2.0.1...v2.1.0)

---
updated-dependencies:
- dependency-name: yaml
  dependency-type: direct:production
  update-type: version-update:semver-minor
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Bumps [karma-jasmine](https://github.com/karma-runner/karma-jasmine) from 5.0.0 to 5.0.1.
- [Release notes](https://github.com/karma-runner/karma-jasmine/releases)
- [Changelog](https://github.com/karma-runner/karma-jasmine/blob/master/CHANGELOG.md)
- [Commits](karma-runner/karma-jasmine@v5.0.0...v5.0.1)

---
updated-dependencies:
- dependency-name: karma-jasmine
  dependency-type: direct:development
  update-type: version-update:semver-patch
...

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