Deprecate si prefix

[byroot]

As discussed a while ago in #7835 (comment)

cc @rafaelfranca

[rafaelfranca]

I think it is better to keep the tests and use assert_deprecated block just to make sure we don't break the deprecated code.

[byroot]

I wasn't aware of assert_deprecated. I'll update thanks.

[hakanai]

Hang on, but isn't it still formatting questionably by default in v5.0.0?

irb(main):001:0> include ActionView::Helpers::NumberHelper
=> Object
irb(main):002:0> number_to_human_size(1000000)
=> "977 KB"

I'd expect either "1000 kB" or "1 MB" and wouldn't mind removal of the option if the default behaviour had been correct in the first place...

I can understand not wanting "kiB", "MiB" and the like since not everyone will have seen those before and very few apps would need to use them anyway, but can't we at least have "kB", "MB" and so on computed correctly? If the method is supposed to produce a "human" size, why is it using the base 2 definition of the units?