Issue/1916 fix align issues

[SergioEstevao]

Fixes #1916

This PR fixes the set alignment property on RCTAzteView to avoid conflict condition with the alignment property on the base TextView Class.

To test:

• Open the demo app
• Add a paragraph block
• Write some text
• Set the alignment to Right or Center
• Check if the alignment is set
• Tap Enter
• Check that the alignment stays set on the previous block
• Switch to HTML
• Check that the HTML has the alignment attributes
• Go back to visual and check if the alignment is applied
• Now tap Enter in the middle of the text of the block
• Check that both block keep the alignment.

PR submission checklist:

• I have considered adding unit tests where possible.
• I have considered if this change warrants user-facing release notes and have added them to RELEASE-NOTES.txt if necessary.

[mchowning]

Working well!

Why do you think didSet was causing the problem? I'm just curious.

[SergioEstevao]

@mchowning I didn't fully tracked down the issue, but it looked like when we were using didSet we were calling super.setAlignment and that was causing the value being set on the base UITextView and then I think the didSet on TextView didn't track down properly the oldValue difference.

In either case, I don't think we were doing the correct step of calling a super.setTextAlignment on a didSet.