[New] stringify/parse: add encodeDotKeys/decodeDotKeys respectively to allow . in object keys

[aks-]

Previously the dot in the keys would be encoded but the round-tripping was broken. Here is the previous behavior

const opts = { allowDots: true };
qs.parse(qs.stringify({ "name.obj": { "first": "John", "last": "Doe" } }, opts), opts)
 // => { name: { obj: { first: 'John', last: 'Doe' } } }

This PR fixes the above behavior and fixes #249:

 qs.parse(qs.stringify({ "name.obj": { "first": "John", "last": "Doe" } }, { allowDots: true, encodeDotKeys: true }), { allowDots: true, decodeDotKeys: true })
{ 'name.obj': { first: 'John', last: 'Doe' } }

[aks-]

@ljharb I wonder if we need allowDots to be true for encodeDotKeys and decodeDotKeys work. Also I can not think of any other name that is similar for parse and stringify method. Any suggestions?

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.81%. Comparing base (5f0449f) to head (867fc7b).

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Additional details and impacted files

@@           Coverage Diff           @@
##             main     #488   +/-   ##
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  Coverage   99.81%   99.81%           
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  Files           9        9           
  Lines        1600     1645   +45     
  Branches      187      190    +3     
=======================================
+ Hits         1597     1642   +45     
  Misses          3        3           

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[ljharb]

Please add test cases that use encodeValuesOnly with this option.

[ljharb]

Thanks! This looks good; I can clean up the remaining comments.

[aks-]

@ljharb I realised that allowDots = false & encodeDotInKeys does not break the round-tripping but it does not encode the dot in key. I just pushed a commit which adjusts the tests and always encodes the key if encodeDotInKeys is set to true except for the invalid case where the error would be thrown. Can you please take another look?