[chore] Move missing experimental symbols to xexporterhelper

[mx-psi]

Description

I forgot to move these symbols in #13821.

Link to tracking issue

Relates to open-telemetry/opentelemetry-collector-contrib/pull/42782, which is how I noticed.

Follows #13821

Updates #11143

[codecov]

Codecov Report

❌ Patch coverage is 89.63964% with 23 lines in your changes missing coverage. Please review.
✅ Project coverage is 91.34%. Comparing base (ba0b327) to head (5997df4).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
...xporter/exporterhelper/internal/queuebatch/logs.go	89.06%	6 Missing and 1 partial ⚠️
...orter/exporterhelper/internal/queuebatch/traces.go	89.06%	6 Missing and 1 partial ⚠️
...rter/exporterhelper/xexporterhelper/new_request.go	0.00%	6 Missing ⚠️
...rter/exporterhelper/internal/queuebatch/metrics.go	95.31%	3 Missing ⚠️

❌ Your patch status has failed because the patch coverage (89.63%) is below the target coverage (95.00%). You can increase the patch coverage or adjust the target coverage.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #13868      +/-   ##
==========================================
- Coverage   91.37%   91.34%   -0.04%     
==========================================
  Files         649      652       +3     
  Lines       42653    42665      +12     
==========================================
- Hits        38973    38971       -2     
- Misses       2854     2866      +12     
- Partials      826      828       +2     

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