feat(electron): Use page title/window location for default context in renderers

[bengourley]

Goal

Renderer events should have a default context.

Design

This implementation takes the page title, and falls back to the window location.

Changeset

Since the amount of logic required was so small I felt comfortable augmenting the renderer event data plugin, rather than creating an entire new plugin.

For packaged apps, window.location.pathname is an absolute file path (like stacktraces). I tweaked logic for stackframe project root stripping so it could be referenced from the renderer event plugin rather than duplicated.

Testing

End to end tests added for all the cases I could think of. config.context and setContext() should take precedence.

[github-actions]

@bugsnag/browser bundle size diff

	Minified	Minfied + Gzipped
Before	40.87 kB	12.62 kB
After	40.87 kB	12.62 kB
±	No change	No change

code coverage diff

Ok	File	Lines	Branches	Functions	Statements
✅	/home/runner/work/bugsnag-js/bugsnag-js/packages/plugin-electron-renderer-event-data/renderer-event-data.js	89.47% (+1.97%)	81.25% (+4.33%)	100% (+0%)	90.48% (+1.59%)
🔴	/home/runner/work/bugsnag-js/bugsnag-js/packages/plugin-electron-renderer-strip-project-root/strip-project-root.js	84.21% (+4.21%)	58.33% (-8.34%)	100% (+0%)	86.36% (+3.03%)

Total:

Lines	Branches	Functions	Statements
82.47%(+0.03%)	72.08%(-0.01%)	83.48%(+0.03%)	81.5%(+0.03%)

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