fix: truncate screenshot filenames using byteLength

[flotwig]

• Closes Screenshot file name too long warning when Bytes exceeded #2403

User facing changelog

• Fixed an issue where screenshots could fail because of names that were too long for the filesystem to accept.

Additional details

• now using bytes instead of characters to resize the string
• if an ENAMETOOLONG error is encountered, the string will be further downsized, down to a minimum of 64 bytes after which the error will still be thrown, like described in Truncate file names for screenshots #2635 (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?

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[cypress]

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Test summary

7931 • 0 • 130 • 2

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Run details

Project	cypress
Status	Passed
Commit	dc57c16
Started	Aug 10, 2020 4:16 PM
Ended	Aug 10, 2020 4:22 PM
Duration	06:33 💡
OS	Linux Debian - 10.1
Browser	Multiple

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[jennifer-shehane]

@flotwig I think that we could probably sprinkle in some DEBUG logs into the new logic, so that we can debug in the future about how the truncation is occurring in case some other issue crops up.

Otherwise it looks fine.