[sdk] Add DelegatingProcessor

[CodeBlanch]

Relates to #5255

Changes

• Adds a public DelegatingProcessor<T> class to SDK.

Details & reasoning

We don't stop users from making more derived versions of our built-in processors or wrapping them in other processors. An example of this is #5250.

Users who wrap one of the built-in processors may run into two things:

• ParentProvider won't be set. That will most likely cause issues with Resource resolution.
• SDK may select a less performant LogRecord pool when batching is in play ([logs] Fix pooling issues when wrapping batch export processor #5255).

Because we can't prevent this, what we should do (IMHO) is give a way to do it safely: DelegatingProcessor

Here is how a user could write the FilterProcessor (from #5250) to be safe using DelegatingProcessor:

    internal sealed class FilteringProcessor<T> : DelegatingProcessor<T>
    {
        private readonly Func<T, bool> filter;

        public FilteringProcessor(BaseProcessor<T> inner, Func<T, bool> filter)
           : base(inner)
        {
            this.filter = filter;
        }

        public override void OnEnd(T data)
        {
            // Call the underlying processor
            // only if the Filter returns true.
            if (this.filter(data))
            {
                base.OnEnd(data);
            }
        }
    }

Public API changes

OpenTelemetry.dll:

namespace OpenTelemetry;

+public abstract class DelegatingProcessor<T> : BaseProcessor<T>
+{
+   protected DelegatingProcessor(BaseProcessor<T> innerProcessor) {}
+   public override void OnStart(T data) {}
+   public override void OnEnd(T data) {}
+   protected override bool OnForceFlush(int timeoutMilliseconds) {}
+   protected override bool OnShutdown(int timeoutMilliseconds) {}
+   protected override void Dispose(bool disposing) {}
+}

Merge requirement checklist

• CONTRIBUTING guidelines followed (license requirements, nullable enabled, static analysis, etc.)
• Unit tests added/updated
• Appropriate CHANGELOG.md files updated for non-trivial changes
• Changes in public API reviewed (if applicable)

[TimothyMothra]

My first thought, are there any one-off Processors in the Test projects that this could replace?

[codecov]

Codecov Report

Attention: Patch coverage is 5.00000% with 19 lines in your changes are missing coverage. Please review.

Project coverage is 82.91%. Comparing base (6250307) to head (3115a71).
Report is 98 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5282      +/-   ##
==========================================
- Coverage   83.38%   82.91%   -0.48%     
==========================================
  Files         297      273      -24     
  Lines       12531    11993     -538     
==========================================
- Hits        10449     9944     -505     
+ Misses       2082     2049      -33     

Flag	Coverage Δ
unittests	?
unittests-Solution-Experimental	82.87% <5.00%> (?)
unittests-Solution-Stable	82.58% <5.00%> (?)

Flags with carried forward coverage won't be shown. Click here to find out more.

Files	Coverage Δ
src/OpenTelemetry/Logs/LoggerProviderSdk.cs	92.00% <50.00%> (-0.86%)	⬇️
src/OpenTelemetry/DelegatingProcessor.cs	0.00% <0.00%> (ø)

... and 37 files with indirect coverage changes

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Closed as inactive. Feel free to reopen if this PR is still being worked on.