Accept nullish Rich Text values in PrismicRichText and PrismicText

[angeloashmore]

Accepting nullish values in <PrismicRichText> and <PrismicText> could lead to a better developer experience. When working with API responses, values passed to those components will never be null or undefined. The API should always return at least [] when the field is left empty.

When a document is still being fetched, however, the value passed to the components may not exist yet.

We can detect this within the components and appropriately return null or undefined. We can also opt out of doing any additional processing, ultimately leading to less work being done.

Related: prismicio/prismic-richtext#50

[angeloashmore]

Included in v2.0.0-beta.2