fix(rewriter): make workers self-exit to avoid SIGABRTs

[flotwig]

User facing changelog

• Fixed a bug in experimentalSourceRewriting where Cypress could exit with a SIGABRT instead of exiting normally.

Additional details

• try to let the threads shut themselves down to avoid SIGABRT when calling process.exit with worker_threads active electron/electron#23366
• users were still encountering the SIGABRT when simply using worker.terminate from the main thread, which was the original workaround: Remove regex-based JS/HTML rewriting, switch to AST-based rewriting #7297 (comment)

How has the user experience changed?

PR Tasks

• Have tests been added/updated?
• Has the original issue been tagged with a release in ZenHub?
• [na] Has a PR for user-facing changes been opened in cypress-documentation?
• [na] Have API changes been updated in the type definitions?
• [na] Have new configuration options been added to the cypress.schema.json?

[cypress-bot]

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If any of the following requirements can't be met, leave a comment in the review selecting 'Request changes', otherwise 'Approve'.

User Experience

• The feature/bugfix is self-documenting from within the product.
• The change provides the end user with a way to fix their problem (no dead ends).

Functionality

• The code works and performs its intended function with the correct logic.
• Performance has been factored in (for example, the code cleans up after itself to not cause memory leaks).
• The code guards against edge cases and invalid input and has tests to cover it.

Maintainability

• The code is readable (too many nested 'if's are a bad sign).
• Names used for variables, methods, etc, clearly describe their function.
• The code is easy to understood and there are relevant comments explaining.
• New algorithms are documented in the code with link(s) to external docs (flowcharts, w3c, chrome, firefox).
• There are comments containing link(s) to the addressed issue (in tests and code).

Quality

• The change does not reimplement code.
• There's not a module from the ecosystem that should be used instead.
• There is no redundant or duplicate code.
• There are no irrelevant comments left in the code.
• Tests are testing the code’s intended functionality in the best way possible.

Internal

• The original issue has been tagged with a release in ZenHub.

[cypress]

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Test summary

3451 • 0 • 50 • 0

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Run details

Project	cypress
Status	Passed
Commit	65dd36d
Started	Jun 2, 2020 7:40 PM
Ended	Jun 2, 2020 7:46 PM
Duration	06:47 💡
OS	Linux Debian - 10.1
Browser	Firefox 74

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[thlorenz]

LGTM except I don't understand having message types implemented as flags.
I mean what do you do if two of those booleans are true, i.e. shutdown and another one?
Which one do you honor? Shouldn't message types be exclusive?

I'd have exclusive message types via an enum or string union instead, i.e. Convert | Shutdown or similar.
However this is not directly related to this PR only that every other message type implemented via a non-exclusive boolean flag adds to the complexity down the line.

[flotwig]

agreed @thlorenz, it's a good point to refactor

[JessicaSachs]

Similar feedback to @thlorenz. I think we can merge this, but can we play a refactor story soon? Next sprint or during any downtime?

[cypress-bot]

Released in 4.8.0.

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