adding more named and explicit imports

[miquelbeltran]

Following the proposal in flutter/website#7798 I have added more explicit and named imports on those places I thought it would make sense.

Let me know what you think.

Pre-launch Checklist

• I read the Flutter Style Guide recently, and have followed its advice.
• I signed the CLA.
• I read the Contributors Guide.
• I updated/added relevant documentation (doc comments with ///).
• All existing and new tests are passing.

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[domesticmouse]

I'm wondering if we should just adopt the default of import 'dart:ui' as ui; as opposed to having a mix of as ui and show Name

[domesticmouse]

Also, please update this PR to turn the CI green. =)

[miquelbeltran]

I'm wondering if we should just adopt the default of import 'dart:ui' as ui; as opposed to having a mix of as ui and show Name

makes sense, I will do the change to see how it looks like

[domesticmouse]

Is import 'dart:math' as math; something we do elsewhere? It almost feels like overkill?

[miquelbeltran]

Is import 'dart:math' as math; something we do elsewhere? It almost feels like overkill?

As with the other changes we have done related to flutter/website#7798 none of them are strictly necessary.

I like the idea of having the math dependency as a named import because it allows for easier discoverability, and because the math import has a lot of top level functions and constants, so it doesn't mess with autocomplete. Although, effective Dart doesn't have a recommendation regarding this, and I don't have a strong opinion on this either, so I'm fine to revert the change.