add internal method ToCollection() to Batch

[TimothyMothra]

related to #2361.
pulling a minor change out of #3198.

Changes

• Add internal method ToCollection to Batch

Please provide a brief description of the changes here.

This change is to eliminate the foreach boilerplate code:

foreach (var data in batch)
{
    someCollection.Add(data);
}

For significant contributions please make sure you have completed the following items:

• Appropriate CHANGELOG.md updated for non-trivial changes
• Design discussion issue #
• Changes in public API reviewed

Other options considered

1. do nothing
   this will cause unit tests to have a lot of foreach statements.

2. ToCollection(ICollection<T> someCollection)
   I considered this but decided to imitate Enumerable.ToList which returns the collection.

3. ToList()
   I don't have a strong opinion about the return type. I chose to return ICollection because I see this used more often in this repo.

4. add extension method/class to OpenTelemetry.Tests.Shared
   this would work, but is an extra file that would need to be imported into test projects.
   having this method in the Batch class allows it to access private fields.

[reyang]

Doesn't seem to have a good reason to expose new public API from Batch.

[codecov]

Codecov Report

Merging #3219 (d8deca4) into main (1918e4b) will decrease coverage by 0.15%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main    #3219      +/-   ##
==========================================
- Coverage   85.69%   85.53%   -0.16%     
==========================================
  Files         260      260              
  Lines        9366     9367       +1     
==========================================
- Hits         8026     8012      -14     
- Misses       1340     1355      +15     

Impacted Files	Coverage Δ
src/OpenTelemetry/Batch.cs	98.92% <100.00%> (+0.01%)	⬆️
...entation/ExportClient/OtlpGrpcTraceExportClient.cs	50.00% <0.00%> (-28.58%)	⬇️
...xporter.OpenTelemetryProtocol/OtlpTraceExporter.cs	59.09% <0.00%> (-18.19%)	⬇️
...ter.ZPages/Implementation/ZPagesActivityTracker.cs	97.14% <0.00%> (-2.86%)	⬇️
...metryProtocol/Implementation/ActivityExtensions.cs	88.73% <0.00%> (-2.71%)	⬇️
...nTelemetry/Internal/OpenTelemetrySdkEventSource.cs	73.27% <0.00%> (-0.87%)	⬇️
...ZPages/Implementation/ZPagesExporterEventSource.cs	62.50% <0.00%> (+6.25%)	⬆️

[TimothyMothra]

Doesn't seem to have a good reason to expose new public API from Batch.

changed to internal.
Verified that the tests that need this already have access to internals.