feat: add `fallback` prop to `<PrismicRichText>` which is rendered when given an empty field

[angeloashmore]

Types of changes

• [ ] Chore (a non-breaking change which is related to package maintenance)
• [ ] Bug fix (a non-breaking change which fixes an issue)
• [x] New feature (a non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to change)

Description

This PR adds a fallback prop to <PrismicRichText>. The value given to fallback is rendered when <PrismicRichText> is given an empty field. If a fallback prop is not given, null is rendered (this is the existing functionality).

<PrismicRichText
  field={document.data.richTextField}
  fallback={<p>Empty content</p>}
/>

In this example, <p>Empty content</p> is rendered if document.data.richTextField is empty (i.e. nullish or contains no content).

Checklist:

• [x] My change requires an update to the official documentation.
• [x] All TSDoc comments are up-to-date and new ones have been added where necessary.
• [x] All new and existing tests are passing.

🦎

[codecov-commenter]

Codecov Report

Merging #135 (16484ca) into master (3aeeda5) will not change coverage. The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master     #135   +/-   ##
=======================================
  Coverage   92.67%   92.67%           
=======================================
  Files          16       16           
  Lines         273      273           
  Branches       61       62    +1     
=======================================
  Hits          253      253           
  Misses          5        5           
  Partials       15       15           

Impacted Files	Coverage Δ
src/PrismicRichText.tsx	96.29% <100.00%> (ø)

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[github-actions[bot]]

size-limit report 📦

Path	Size
dist/index.js	4.42 KB (0%)
dist/index.cjs	6.3 KB (-0.02% 🔽)