Move Bidi static methods to instance methods on TextDirection

[DartBot]

<img src="https://avatars.githubusercontent.com/u/444270?v=3" align="left" width="96" height="96"hspace="10"> Issue by seaneagan
Originally opened as dart-lang/sdk#11752

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In package:intl, Bidi acts as a namespace for static methods, which is generally an anti-pattern in dart, since dart libraries can act as namespaces for static methods, so a separate "bidi.dart" library maybe. However, most of these methods are duplicated for both TextDirections (RTL and LTR), so it seems like making them polymorphic to TextDirection would make sense. For a basic idea of what this would look like, see:

https://gist.github.com/seaneagan/5957736

Of course they wouldn't make sense for TextDirection.UNKNOWN, but I don't think TextDirection.UNKNOWN is necessary. I think it would make more sense just to reuse null for that concept.

Another option would be to keep them as static/top-level methods which receive a TextDirection, but that doesn't feel quite as nice.

[DartBot]

<img src="https://avatars.githubusercontent.com/u/5449880?v=3" align="left" width="48" height="48"hspace="10"> Comment by iposva-google

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Added Area-Pkg, Triaged labels.

[DartBot]

<img src="https://avatars.githubusercontent.com/u/5479?v=3" align="left" width="48" height="48"hspace="10"> Comment by sethladd

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cc @alan-knight.
Removed Type-Defect label.
Added Type-Enhancement, Pkg-Intl labels.

[DartBot]

<img src="https://avatars.githubusercontent.com/u/5479?v=3" align="left" width="48" height="48"hspace="10"> Comment by sethladd

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Do we intend to do this? If not, can we close?

[DartBot]

<img src="https://avatars.githubusercontent.com/u/3476088?v=3" align="left" width="48" height="48"hspace="10"> Comment by alan-knight

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I'd say close. It's probably a good idea, but I don't think people tend to use those methods explicitly, so it doesn't seem worth the work to re-arrange. We have a lot bigger things that need work.

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Added WontFix label.