refactor(item): replaced attributes with item-start / item-end

[AmitMY]

Short description of what this resolves:

Ambiguity in RTL projects.
Issue:
#11124

Changes proposed in this pull request:

• Change item-left to item-start
• Change item-right to item-end
• Deprecated SCSS variables with -item-left and created -item-start. same for right/end

Ionic Version: 3.1.x

[manucorporat]

Well, we can easily make this a non-breaking change.

• Let's add item-left and item-right back (as a deprecated util)
• We could add some logic to Item, so it prints a warning message when people use item-right or item-left.

[AmitMY]

@manucorporat That is possible, although, I have no idea what to do with:
https://github.com/AmitMY/ionic/blob/cb5ac7cfc1e2a9d49c2a696c120b37e4e3934500/src/components/item/item.ts#L277
https://github.com/AmitMY/ionic/blob/cb5ac7cfc1e2a9d49c2a696c120b37e4e3934500/src/components/item/item.ts#286

And where exactly to add the deprecation message.

The other thing for support, is just the 16 .scss files, which are easy fixes.

Do I also need to add /** @deprecated **/ above .scss selectors/variables that are deprecated? because I can't make someone not use the old .scss variables.

[brandyscarney]

I think this should behave the same everywhere:

left - Always left regardless of dir
right - Always right regardless of dir
start - The same as left if direction is left-to-right and right if direction is right-to-left.
end - The same as right if direction is left-to-right and left if direction is right-to-left.

This would make it so there are no breaking changes, and it improves support.

[AmitMY]

@brandyscarney While I agree with you on text-X, icon-X, side for menu and for sliding item, I disagree on this one.
The item's left and right are very strict things as far as I see them (currently, left is a separate container, while right is inside the main container etc, and those are not just rules)

On this one, I really believe there should be a deprecation for left and right.

Side note: I've seen you reviewed most rtl PRs. Can you please review this one as well? #11121