Add support for running tagged test files

[kostadin-damyanov-prime]

Hello.

This PR adds support for --tags option for the test command.
This way we can tag test files with the @Tags annotation like dart's test suite does.
Using this option we can now run only the test files matching a given tag or a list of tags.

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[mateuszwojtczak]

Hi @kostadin-damyanov-prime, thanks a lot for making this contribution! We have just discussed tags internally :)

I have a few questions:

1. Should we lock the analyzer package version to some more specific than any? ok, solved
2. When I initially considered tags, I was thinking about somehow connecting to the official test_api way of doing that. I can see you implemented a separate mechanism for that. WDYT?

[kostadin-damyanov-prime]

@mateuszwojtczak Hi.

1. Done.
2. I am not too familiar with test_api. Do they use a different approach? If there is some code that we can reuse I am all for it.

[mateuszwojtczak]

Yes, look at this information in their readme.

They also support dart_test.yaml file. Your implementation is really fine with most cases and it's simple which is very beneficial.

I'm just worried that the community would assume that Patrol uses the same tags as Dart/Flutter tests. This is a very frequent assumption that ends with people filing issues, because they assume Patrol uses the same approach. Although we can't always be 100% compatible with that approach, we still at least try to do so.

[kostadin-damyanov-prime]

I agree that mplementation based on test_api will be more feature-rich. Maybe even supporting stuff like --exclude-tags and boolean selectors. Unfortunately we do not have the time to implement it now. You can either merge this PR or do implementation based on test_api yourself. We (and anyone else) can use this fork in the meantime.

[mateuszwojtczak]

@kostadin-damyanov-prime We decided to implement tags and skips by passing them as arguments to the patrolTest function. This means we are no longer in need of annotations / other analyzer pre-processing work.

Thus, I'm closing this PR and we're gonna solve #492 with another approach :)