Introduce TelemetryListener

[martintmk]

Details on the issue fix or feature implementation

Introduce TelemetryListener API that is used to listen for telemetry events. As opposed to DiagnosticSource that only accepts object-based arguments, this listener allows generics.

This enables us to simplify the Polly.Core and convert all argument classes to structs and drop all pooling of these arguments.

For context:
#1233 (comment)

Confirm the following

• I started this PR by branching from the head of the default branch
• I have targeted the PR to merge into the default branch
• I have included unit tests for the issue/feature
• I have successfully run a local build

[codecov]

Codecov Report

Merging #1486 (d441426) into main (4a8c59a) will decrease coverage by 0.14%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main    #1486      +/-   ##
==========================================
- Coverage   83.85%   83.71%   -0.14%     
==========================================
  Files         277      272       -5     
  Lines        6478     6424      -54     
  Branches     1016     1012       -4     
==========================================
- Hits         5432     5378      -54     
  Misses        837      837              
  Partials      209      209              

Flag	Coverage Δ
linux	83.71% <100.00%> (-0.14%)	⬇️
macos	83.71% <100.00%> (-0.14%)	⬇️
windows	?

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

Files Changed	Coverage Δ
...ly.Core/CircuitBreaker/OnCircuitClosedArguments.cs	100.00% <ø> (ø)
...ore/CircuitBreaker/OnCircuitHalfOpenedArguments.cs	100.00% <ø> (ø)
...ly.Core/CircuitBreaker/OnCircuitOpenedArguments.cs	100.00% <ø> (ø)
src/Polly.Core/Hedging/OnHedgingArguments.cs	100.00% <ø> (ø)
src/Polly.Core/Retry/OnRetryArguments.cs	100.00% <ø> (ø)
src/Polly.Core/Timeout/OnTimeoutArguments.cs	100.00% <ø> (ø)
...rc/Polly.Core/Timeout/TimeoutGeneratorArguments.cs	100.00% <ø> (ø)
...lly.RateLimiting/OnRateLimiterRejectedArguments.cs	100.00% <ø> (ø)
.../Polly.Core/Fallback/FallbackResilienceStrategy.cs	100.00% <100.00%> (ø)
.../Polly.Core/Registry/ResiliencePipelineRegistry.cs	100.00% <100.00%> (ø)
... and 14 more