Verify that accessibilityTraits values are valid

[Jani Eväkallio]

Valid values documented here:
https://facebook.github.io/react-native/docs/accessibility.html#accessibilitytraits-ios

[Alex Saunders]

@jevakallio should we expand this issue to verify that accessibilityComponentType values are valid (one of either 'none', 'button', 'radiobutton_checked' or 'radiobutton_unchecked') as it's the android version of accessibilityTraits? or should that be a separate issue?

cc: @knitcodemonkey

[Jani Eväkallio]

Let's split this out to a separate issue and a separate rule.

I imagine the implementation will be mostly the same, but I can also think of cases where someone may want to check for one and not the other (e.g. app only supports one platform).

[Alex Saunders]

Cool, should have a branch ready to PR for this issue then