fix(coverage): v8 browser memory leak between test files

[AriPerkkio]

Description

Resolves #11447

As V8 coverage starts profiler, we end up collecting stuff between test files that share same V8 instance (tab). Currently we are not toggling coverage on-off between test files, as that used to break the results. It seems that collecting garbage between coverage toggling fixes this.

This has a performance hit of course, but it's more correct behavior. Running https://github.com/vitest-tests/coverage-large locally on M2 Air:

• vitest@5.0.3: 0m36.104s, 0m33.941s
• This PR on pkg.pr.new, 2953e5c: 0m40.244s, 0m41.833s

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[pkg-pr-new]

@vitest/browser

npm i https://pkg.pr.new/@vitest/browser@2953e5c

@vitest/browser-playwright

npm i https://pkg.pr.new/@vitest/browser-playwright@2953e5c

@vitest/browser-preview

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@vitest/coverage-istanbul

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@vitest/coverage-v8

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@vitest/expect

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@vitest/mocker

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@vitest/pretty-format

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@vitest/snapshot

npm i https://pkg.pr.new/@vitest/snapshot@2953e5c

@vitest/spy

npm i https://pkg.pr.new/@vitest/spy@2953e5c

@vitest/ui

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@vitest/utils

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vitest

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@vitest/web-worker

npm i https://pkg.pr.new/@vitest/web-worker@2953e5c

commit: 2953e5c

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[AriPerkkio]

Failure without the fix:

And yes, this test passes fine when fix is reverted and coverage is disabled.