[Go SDK]: Retrieve file size in CreateInitialRestriction in textio.Read

[johannaojeling]

Fixes #25532 and refactors textio.Read to retrieve the file's size in readFn.CreateInitialRestriction instead of in a separate DoFn.

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[codecov]

Codecov Report

Merging #25535 (9867810) into master (977e531) will decrease coverage by 0.01%.
The diff coverage is 62.50%.

@@            Coverage Diff             @@
##           master   #25535      +/-   ##
==========================================
- Coverage   72.66%   72.66%   -0.01%     
==========================================
  Files         759      759              
  Lines      100689   100685       -4     
==========================================
- Hits        73168    73160       -8     
- Misses      26112    26116       +4     
  Partials     1409     1409              

Flag	Coverage Δ
go	52.11% <62.50%> (-0.01%)	⬇️

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Impacted Files	Coverage Δ
sdks/go/pkg/beam/io/textio/textio.go	54.21% <62.50%> (-0.95%)	⬇️
...eam/runners/portability/fn_api_runner/execution.py	92.49% <0.00%> (-0.64%)	⬇️

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[lostluck]

Run Go PostCommit

[lostluck]

Technically it no longer relies on an input size in bytes. We can to remove that part of the comment now.

[johannaojeling]

Good catch, thanks!

[lostluck]

LGTM other than the comment update!

Thank you very kindly!