feat: Add 'slowTestThreshold' and fix this.slow() inside specs

[BlueWinds]

• Closes Cypress should set a mocha slow threshold for more reasonable reporting #447

User facing changelog

• Adds slowTestThreshold config option to customize slow test threshold
• BREAKING: Changes the default slow test threshold from 75ms (mocha's default) to 10000ms. In the default spec reporter, this will hide test timing for any test under 5000ms. To restore the old behavior, you can add "slowTestThreshold": 75 to your cypress configuration.

Additional details

A test that executes for half of the “slowTestThreshows” time will be highlighted in yellow with the default spec reporter; a test that executes for entire “slow” time will be highlighted in red. This is a visual change only - slow tests still pass. See https://mochajs.org/#-slow-ms-s-ms for more details.

PR Tasks

• Have tests been added/updated? I have added some relevant unit tests, but welcome further suggestions.
• Has the original issue or this PR been tagged with a release in ZenHub?
• Has a PR for user-facing changes been opened in cypress-documentation? Add documentation for new slowTestThreshold config option cypress-documentation#4145 requires reworking
• Have API changes been updated in the type definitions?
• Have new configuration options been added to the cypress.schema.json?

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[cypress]

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Test summary

4204 • 0 • 50 • 2 • 2

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Run details

Project	cypress
Status	Passed
Commit	30bd7ae
Started	Oct 14, 2021 5:16 PM
Ended	Oct 14, 2021 5:25 PM
Duration	09:40 💡
OS	Linux Debian - 10.9
Browser	Chrome beta 95

View run in Cypress Dashboard ➡️

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Flakiness

	cypress/integration/cypress/proxy-logging-spec.ts		2
1	Proxy Logging > request logging > xhr log has response body/status code
2	... > works with forceNetworkError

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[BlueWinds]

After struggling with it for a bit, I've eventually decided not to throw errors if the user uses this.slow() - Mocha calls it internally in several circumstances, and distinguishing them from user-written calls grew too complicated to warrant the effort over simply leaving it a no-op.

[flotwig]

Nice 👍

[BlueWinds]

Latest commit fixes this.slow() inside tests, and greatly simplifies how slowTestThreshold is handled. It also changes the default spec reporter to always show test timings, even for fast tests.

Still TODO:

• Add tests around this functionality
• Move slowTestThreshold to be e2e/component specific rather than a global value

[chrisbreiding]

Other than the nitpicks about yellow vs orange, looks great.