YaruPageIndicator: add custom scale parameters

[d-loose]

Allows to customize the size and spacing of YaruPageIndicator's dots:

Screencast.from.2023-02-22.12-48-53.webm

Fix #622

Pull request checklist

• This PR does not introduce visual changes, or
  • I ran flutter test --update-goldens and committed the changes if there were any, or
  • I added before/after/light/dark screenshots if the visual changes I made were not covered by golden tests.

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[Feichtmeier]

Looks good because it works 😄

As I do not care enough for the implementation detail let @jpnurmi and @Jupi007 double check as they are usually a bit more nit-picky

[Jupi007]

I agree that provide a way to customize dot size and spacing is a great idea!

But the way I implemented the current spacing was preventing layout overflow, while this PR doesn't provide any kind of security:

Peek.22-02-2023.13-25.mp4

@d-loose Can you implement a way to avoid overflow?

Also it would be nice that your new properties could not be factors, but real size:

final double dotSize = 12.0;
final double dotSpacingTarget; // target, because it can be stretched cause to the overflow guard

It is more intuitive in that way, and so we don't hide those parameters with some obscure internal stuff.

[jpnurmi]

As a user, I'd rather specify the desired size and spacing than a factor because I don't know what the factor applies to :)

[d-loose]

Thanks!
Vertical constraints are respected again, and I've changed the parameters to accept absolute values.

Screencast.from.2023-02-22.13-51-39.webm

[Jupi007]

I can't actually test it, but if you ensure me there's no more vertical overflow, then LGFM 🙂 👍

[d-loose]

I can :)
It only happened before, because I recklessly rescaled maxWidth 😆