Introduce a parameter to -unittest that lets you filter out unittests…

[maxhaton]

… from modules that aren't listed explicitly on the command line.

For example -i foo.d should only run unittests from foo but not anything foo imports and thus compiles because of -i

[dlang-bot]

Thanks for your pull request, @maxhaton!

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Testing this PR locally

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dub run digger -- build "master + dmd#15796"

[maxhaton]

Haven't thought about testing this yet.

UDAs are a sketch I couldn't be bothered to finish implementing.

[maxhaton]

@atilaneves @adamdruppe @deadalnix quick sketch to prove you can do it. May be intractable for some subtle reason.

[Imperatorn]

Errors in globals.d

[RazvanN7]

@maxhaton what's your plan with this PR? Maybe add some tests first?