Add defaultValue and initialValue

[PerfectPixel]

Hey Erik,

today I needed to set an initialValue on the array, which led to a weird workaround for me. So here the PR:

I copied the explanation from the react-final-form repository, and also added the defaultValue.

I though about checking that the values are array but then decided against it. Maybe it would make sense to pass all the other props through too?

Cheers!

[codecov]

Codecov Report

Merging #98 into master will not change coverage.
The diff coverage is n/a.

@@          Coverage Diff          @@
##           master    #98   +/-   ##
=====================================
  Coverage     100%   100%           
=====================================
  Files           6      6           
  Lines          60     60           
  Branches       10     10           
=====================================
  Hits           60     60

Impacted Files	Coverage Δ
src/useFieldArray.js	100% <ø> (ø)	⬆️
src/FieldArray.js	100% <ø> (ø)	⬆️

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[PerfectPixel]

I noticed that using initialValue with useFieldArray leads to react constantly updating. Maybe you have an idea what causes it @erikras

Edit: I realized that it was an error caused by always creating new array references on render

[erikras]

Can you add these two to index.d.ts, too?

[PerfectPixel]

I could, but isn't that redundant as UseFieldArrayConfig<FieldValue> extends UseFieldConfig<FieldValue> and UseFieldConfig already contains initialValue and defaultValue 🤔

Edit:
I just checked in my typescript project, all properties of useField are also available in useArrayField within the type although only a few are passed through. Which brings me back to:

Maybe it would make sense to pass all the other props through too?

[PerfectPixel]

@erikras any decision on my question above? 🙃

[erikras]

Published in v3.1.1.