Add snake-key decoding strategy for URLQuery

[MahdiBM]

Adds snake-key decoding strategy for URLQuery.
Matches Foundation's JSONDecoder implementation although i found like 3 different key-handling bugs in that implementation while writing this.

[MahdiBM]

I thought my misclick is merging the PR to main without a review 😵‍💫

[0xTim]

It can't until it's had an approval

[codecov-commenter]

Codecov Report

Merging #3094 (5673062) into main (3bf4e73) will increase coverage by 0.08%.
Report is 2 commits behind head on main.
The diff coverage is 100.00%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3094      +/-   ##
==========================================
+ Coverage   76.23%   76.32%   +0.08%     
==========================================
  Files         211      211              
  Lines        7904     7963      +59     
==========================================
+ Hits         6026     6078      +52     
- Misses       1878     1885       +7     

Files	Coverage Δ
...ces/Vapor/Authentication/AuthenticationCache.swift	84.84% <100.00%> (+0.97%)	⬆️
Sources/Vapor/Authentication/Authenticator.swift	57.89% <ø> (ø)
Sources/Vapor/Authentication/GuardMiddleware.swift	100.00% <ø> (ø)
...rces/Vapor/Authentication/RedirectMiddleware.swift	83.33% <ø> (ø)
Sources/Vapor/Error/AbortError.swift	74.41% <ø> (ø)
...s/Vapor/URLEncodedForm/URLEncodedFormDecoder.swift	88.65% <100.00%> (+2.87%)	⬆️
Sources/Vapor/Utilities/BasicCodingKey.swift	33.33% <ø> (ø)

... and 2 files with indirect coverage changes

[MahdiBM]

hmm that didn't turn out like i was thinking it would 🤔 just caused a bunch of whitespace changes for the most part