src: use simdjson

[himself65]

Fixes: #59288

[codecov]

Codecov Report

❌ Patch coverage is 79.74684% with 16 lines in your changes missing coverage. Please review.
✅ Project coverage is 89.97%. Comparing base (91dadf2) to head (111b1c2).
⚠️ Report is 16 commits behind head on main.

Files with missing lines	Patch %	Lines
src/json_parser.cc	79.74%	4 Missing and 12 partials ⚠️

Additional details and impacted files

@@ Coverage Diff @@## main #59308 +/- ##
==========================================
- Coverage 90.00% 89.97% -0.03% 
==========================================
Files 649 649 Lines 192180 192192 +12 Branches 37659 37684 +25 ==========================================
- Hits 172970 172933 -37 + Misses 11830 11829 -1 - Partials 7380 7430 +50 

Files with missing lines	Coverage Δ
src/json_parser.h	100.00% <ø> (ø)
src/json_parser.cc	74.75% <79.74%> (-5.25%)	⬇️

... and 32 files with indirect coverage changes

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[joyeecheung]

Actually reading this I realized that if we are moving towards simdjson, it's better to just use simdjson directly in the callsite instead of shimming JSONParser over it, because simdjson does not really support random access, unlike the current JSON parser interface. As a result trying to shim it is bound to lead to repetitive parsing like what's happening here. The correct way to handle fields of unknown order is to just iterate over the fields and handle them for different specific key values on an ad-hoc basis, as suggested by the simdjson documentation: https://github.com/simdjson/simdjson/blob/master/doc/basics.md#using-the-parsed-json

For example, for SEA, this would be the recommended way to parse the document according to the simdjson documentaiton: #59323