Allow readonly arrays as inputs

[diesieben07]

What:
The items parameter of matchSorter as well as the keys option are being changed to ReadonlyArray from a plain Array. This more closely represents the contract of the function, as it does not modify these arrays.
Fixes #128.

Why:
Even though matchSorter does not modify its input array, it cannot be called with a value of type ReadonlyArray:

const input: readonly string[] = ['foo', 'bar', 'baz'];
matchSorter(input, 'f'); // does not compile

How:
The required changes are simple: The input types are changed to ReadyonlyArray. This is not a breaking change, as Array is a subtype of ReadonlyArray in typescript, so "normal arrays" can be passed in like before.

Checklist:

• Documentation N/A - The fact a new array is returned is already present in the documentation
• Tests N/A
• Ready to be merged
  

[codecov]

Codecov Report

Merging #129 (3a49b43) into main (fba154b) will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff            @@
##              main      #129   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files            1         1           
  Lines          163       163           
  Branches        39        39           
=========================================
  Hits           163       163           

Impacted Files	Coverage Δ
src/index.ts	100.00% <ø> (ø)

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[kentcdodds]

@all-contributors please add @diesieben07 for code

[allcontributors]

@kentcdodds

I've put up a pull request to add @diesieben07! 🎉

[github-actions]

🎉 This PR is included in version 6.3.1 🎉

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

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