perf(bundle): merge duplicate selectors with dir attribute

[AmitMY]

This will get more effective after each new directional mixin. Like #11635, #11649, etc..

I am not sure of more places that need this pipe, perhaps in app-scripts or something. Either let me know, or merge this and we will figure it out after

Short description of what this resolves:

Increased bundle size as a result of multiple duplicated selectors created for directional support

Changes proposed in this pull request:

• add a gulp pipe for merging directional selectors
• add dev package gulp transform

Ionic Version: 3.x

[Ionitron]

Hello and thank you for contributing to Ionic! We have been working on porting all of the Ionic components to web components and have recently updated master to reflect this. This significant change has caused this pull request to break. While we really appreciate the time and effort you put into creating this, we are not able to merge it because of the newly introduced conflicts. We are extremely sorry about this. We will not be merging any more features in to v3. If this is a feature and you have the time, please resubmit this PR against the master branch. If this is a critical security issue in v3, we would greatly appreciate it if you would resubmit the PR against the new v3 branch. Thanks so much for your time!