Use deterministic culture when converting to string

[bkoelman]

Although there's currently no code in JsonApiDotNetCore that uses RuntimeTypeConverter for converting to string, it's a public type. So its behavior should be deterministic and not depend on the OS-level culture settings.

QUALITY CHECKLIST

• Changes implemented in code
• Complies with our contributing guidelines
• N/A: Adapted tests
• N/A: Documentation updated

[codecov]

Codecov Report

Merging #1267 (d27b2f5) into master (9a2f364) will not change coverage.
The diff coverage is 100.00%.

❗ Current head d27b2f5 differs from pull request most recent head db852cf. Consider uploading reports for the commit db852cf to get more accurate results

@@           Coverage Diff           @@
##           master    #1267   +/-   ##
=======================================
  Coverage   92.67%   92.67%           
=======================================
  Files         243      243           
  Lines        7814     7814           
=======================================
  Hits         7242     7242           
  Misses        572      572           

Impacted Files	Coverage Δ
...tations/Resources/Internal/RuntimeTypeConverter.cs	100.00% <100.00%> (ø)

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