Relax transform coder equality

[RustedBones]

Streaming pipeline using coders created with xmap fail to update with:

Workflow failed. Causes: The new job is not compatible with xxx. The original job (if it existed) has not been aborted., The Coder or type for step xxx has changed.

TransformCoder was defined the same way as DelegateCoder from beam, making sure underlying functions were equal.

This is very unlikely that user define several coders with same type signature with xmap (and will likely result in implicit conflict).

Relax the serialization/equality so pipeline upgrade pass the validation.

[codecov]

Codecov Report

Merging #4780 (a68777a) into main (01ca7c8) will decrease coverage by 0.04%.
The diff coverage is 100.00%.

❗ Current head a68777a differs from pull request most recent head 475b7b2. Consider uploading reports for the commit 475b7b2 to get more accurate results

@@            Coverage Diff             @@
##             main    #4780      +/-   ##
==========================================
- Coverage   61.21%   61.18%   -0.04%     
==========================================
  Files         286      286              
  Lines       10562    10553       -9     
  Branches      773      769       -4     
==========================================
- Hits         6466     6457       -9     
  Misses       4096     4096              

Impacted Files	Coverage Δ
...in/scala/com/spotify/scio/values/SCollection.scala	94.02% <ø> (ø)
...src/main/scala/com/spotify/scio/coders/Coder.scala	85.26% <100.00%> (-0.39%)	⬇️
...a/com/spotify/scio/util/random/RandomSampler.scala	96.42% <100.00%> (ø)
...y/scio/values/PairSkewedSCollectionFunctions.scala	96.85% <100.00%> (-0.08%)	⬇️

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