[Prometheus] Split up projects based on hosting mechanism.

[Yun-Ting]

Fixes #3057.

Changes

Addressing some comments in #3375.
There are some big commits got merged over the course of the development of PR3375 and I figured starting from the more current main line is easier than resolving merge conflicts.

The updated project setup is as follows:

• OpenTelemetry.Exporter.Prometheus.Shared contains the PrometheusExporter, PrometheusExporterOptions and serialization methods for all the shared classes to both AspNetCore and HttpListener projects. This project is not expected to be consumed directly by the end users. It serves as a clean way to group shared code for the below 2 projects for semantic reasons. As a result, I've deleted the Implementation folder that was in OpenTelemetry.Exporter.Prometheus project, and moved out the shared files which was previously in the folder to be the immediate children of the project.

• OpenTelemetry.Exporter.Prometheus.HttpListener contains the PrometheusHttpListener and its options class. It aims to provide end users a quick setup experience for using OTel metrics with Prometheus Exporter locally.

• OpenTelemetry.Exporter.Prometheus.AspNetCore contains the middleware and its extensions for registering. This is for users trying to run PrometheusExporter in production environment.

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

[codecov]

Codecov Report

Merging #3430 (2f75b66) into main (2b1e75d) will increase coverage by 0.25%.
The diff coverage is 73.33%.

❗ Current head 2f75b66 differs from pull request most recent head 4f5449f. Consider uploading reports for the commit 4f5449f to get more accurate results

@@            Coverage Diff             @@
##             main    #3430      +/-   ##
==========================================
+ Coverage   86.25%   86.50%   +0.25%     
==========================================
  Files         272      275       +3     
  Lines        9939     9977      +38     
==========================================
+ Hits         8573     8631      +58     
+ Misses       1366     1346      -20     

Impacted Files	Coverage Δ
.../PrometheusExporterApplicationBuilderExtensions.cs	100.00% <ø> (ø)
...rometheusExporterEndpointRouteBuilderExtensions.cs	100.00% <ø> (ø)
...metheus.AspNetCore/PrometheusExporterMiddleware.cs	67.85% <ø> (ø)
...etheus.HttpListener/PrometheusCollectionManager.cs	78.04% <ø> (ø)
...heus.HttpListener/PrometheusExporterEventSource.cs	27.77% <ø> (ø)
...ometheus.HttpListener/PrometheusExporterOptions.cs	57.14% <ø> (ø)
...er.Prometheus.HttpListener/PrometheusSerializer.cs	78.21% <ø> (ø)
...Prometheus.HttpListener/PrometheusSerializerExt.cs	100.00% <ø> (ø)
...orterHttpListenerMeterProviderBuilderExtensions.cs	57.14% <57.14%> (ø)
....Prometheus.HttpListener/PrometheusHttpListener.cs	81.57% <87.50%> (ø)
... and 14 more

[utpilla]

We don't need to run publicApi analyzer for the shared project. This might require adding some new condition in Common.prod.props. Currently, publicApi analyzer is run for every project under src/.

[Yun-Ting]

#3497

[utpilla]

LGTM. Left some minor suggestions.

[CodeBlanch]

A few nits but LGTM

[cijothomas]

may need to be changed to more specific

[cijothomas]

questionable why aspnetcore.tests need special access.

[Yun-Ting]

It's because of this https://github.com/open-telemetry/opentelemetry-dotnet/blob/main/test/OpenTelemetry.Exporter.Prometheus.AspNetCore.Tests/PrometheusCollectionManagerTests.cs#:~:text=if%20(!provider.TryFindExporter(out%20PrometheusExporter%20exporter))

[cijothomas]

not sure ns need a change here? The class name already have Prometheus in it..

[cijothomas]

the ns already has prometheus in it, so class name again having prometheus is bit looong.

[cijothomas]

Merging to make progress. Rest of the comments can be addressed as follow ups.