[exporterhelper] Deprecate RequestSizer

[mx-psi]

Description

Deprecates an unused type. As can be seen in https://github.com/search?q=%2FRequestSizer%5Cb%2F+-is%3Afork+language%3AGo+NOT+repo%3Arpradeepkumar7%2Ffirst-opentelemetry-exporter&type=code&l=Go it is not used anywhere, inside or outside of this repository

Link to tracking issue

Updates #11143

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 91.44%. Comparing base (66f2c45) to head (4170014).
⚠️ Report is 6 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #13804      +/-   ##
==========================================
+ Coverage   91.43%   91.44%   +0.01%     
==========================================
  Files         640      640              
  Lines       42665    42665              
==========================================
+ Hits        39009    39017       +8     
+ Misses       2836     2830       -6     
+ Partials      820      818       -2     

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[bogdandrutu]

Please don't do this since they are planned to be used.

The whole idea is to allow other exporters to have different implementations of the Request object, and things like The RequestErroHandler type is used to communicate between the export function and the retry mechanism in case partial retries are needed.

I am OK if we want to drop the whole idea of supporting custom implementation for the Request then a larger cleanup is needed, otherwise we should let these helpers public so custom implementation can use.

[mx-psi]

@bogdandrutu I am going to do a bigger refactor and e.g. move the New*Request methods to xexporterhelper. However, I wanted to deal with these two independently because:

1. RequestSizer is not used at all, neither within opentelemetry-collector or outside of it https://github.com/search?q=org%3Aopen-telemetry+%2FRequestSizer%5Cb%2F&type=code
2. RequestErroHandler is used only internally and it's functionality seems independent from the rest of the code.

I can just move RequestErrorHandler to xexporterhelper, but I do think we can just remove RequestSizer, it is not used at all.

[mx-psi]

I changed it so that we only remove RequestSizer which is completely unused.

[mx-psi]

#13821 moves all Experimental symbols to xexporterhelper.

[bogdandrutu]

I changed it so that we only remove RequestSizer which is completely unused.

In QueueBatchSettings you can see there are some arguments like ItemsSizer which I think is the RequestSizer type

[mx-psi]

Okay, I see. I did not realize we were using type aliases in that way.

I will then suggest we move this to xexporterhelper. Let's continue the discussion over at #13821