Allow project filtered test runs to report coverage of only filtered projects #6331

Clear and concise description of the problem

Currently running vitest run --coverage --project <project_a> will result in all other projects reporting no coverage.

Suggested solution

Report only the coverage of the filtered projects when using the --project flag.

Alternative

By default, set the all flag to false if using --project (not quite the same but close)

Additional context

Getting accurate project coverage while testing in a monorepo is hard and you have to resort to npm run cover -w <project_a> which generates a coverage folder that isn't ignored by default at the project level.

Closest I have gotten is using the all:false flag which still doesn't quite do what I'm looking for

Validations

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