Refactor right buttons

This pr started with an attempt to eliminate button flickering entirely when updating buttons which contain react components via mergeOptions. While the attempt wasn't 100% successful, I dit get some insights in the process.

* It's not possible to add buttons at specific indices. Buttons contain an order property which determines the order of the button in the TopBar. To somewhat overcome this limitation, we can let users control button order via options.

* When a right most component button is replaced with another component button, the rest of the buttons shift to the right since the newly added component isn't measured when it's added to the menu and its width is zero. 
We usually handle this situation with the `waitForRender` option but since buttons are measured with `MeasureSpec.UNSPECIFIED`, their dimensions are zero. Because of this, I've added options to set button dimensions.

* When updating buttons via mergeOptions, if a component button is already added to the menu with the same order we will not remove and added it again. This mitigates flickering in some situations.

* Textual button style properties were applied by traversing the view hierarchy and searching for the TextView corresponding to the button and updating its styles directly.
There was an inherent bug in this logic where if two buttons contained the same text, styles could have been applied to the wrong TextView. We now apply styles directly on the button using spans.