[IxSelect]: Support for Angular Forms

[Tiagogv]

Pull request checklist

Please check if your PR fulfills the following requirements:

• Tests for the changes have been added (for bug fixes / features)
• Docs have been reviewed and added / updated if needed (for bug fixes / features)
• Build (yarn build) was run locally and any changes were pushed
• Unit tests (yarn test) were run locally and passed
• Visual Regression Tests (yarn visual-regression) were run locally and passed
• Linting (npm lint) was run locally and passed

Pull request type

Please check the type of change your PR introduces:

• Bug fix
• Feature
• Refactoring (no functional changes, no API changes)
• Build related changes
• Documentation content changes
• Other (please describe):

What is the current behavior?

GitHub Issue Number: closes #736

What is the new behavior?

• Added valueAccessorConfigs for ix-select to angular output target
• Change selectedIndices to value in order to work with Stencil's generated ValueAccessor. Backward compatibility was added. Deprecated selectedIndices.
• Change itemSelectionChange to valueChange (Backward compatibility added). valueChange now emits a single value if mode='single' and an array if mode='multiple'. This is more close aligned with the default behavior of a native select element. Deprecated itemSelectionChange.

Does this introduce a breaking change?

• Yes
• No

Testing

• Tested the generated angular component with [ngModel].
• Tested the web component to make sure behavior did not changed in all modes ('single', 'multiple' and 'editable')

Other information