Avoid Outcome<T> to Outcome conversion when not necessary

[martintmk]

Details on the issue fix or feature implementation

This PR introduces new internal helpers that are used in individual strategies.

• EventInvoker
• GeneratorInvoker
• PredicateInvoker

These classes use generic and non-generic delegates and adopt them to a generic methods:

Usage:

// non-generic options
var options = new RetryStrategyOptions(); 
PredicateInvoker<ShouldRetryArguments>.NonGeneric(options.ShouldRetry);
EventInvoker<OnRetryArguments>.NonGeneric(options.OnRetry);
GeneratorInvoker<RetryDelayArguments, TimeSpan>.NonGeneric(options.RetryDelayGenerator);

// or generic
var options = new RetryStrategyOptions<string>(); 
PredicateInvoker<ShouldRetryArguments>.Generic(options.ShouldRetry);
EventInvoker<OnRetryArguments>.Generic(options.OnRetry);
GeneratorInvoker<RetryDelayArguments, TimeSpan>.Generic(options.RetryDelayGenerator);

These reduce some duplications we have and provide nice perf boost in strategies. I'll follow up in other strategies.

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-commenter]

Codecov Report

Merging #1229 (0131cd4) into main (38f9870) will increase coverage by 0.05%.
The diff coverage is 100.00%.

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@@            Coverage Diff             @@
##             main    #1229      +/-   ##
==========================================
+ Coverage   82.85%   82.91%   +0.05%     
==========================================
  Files         264      267       +3     
  Lines        6119     6139      +20     
  Branches      978      979       +1     
==========================================
+ Hits         5070     5090      +20     
  Misses        844      844              
  Partials      205      205              

Flag	Coverage Δ
linux	82.91% <100.00%> (+0.05%)	⬆️
macos	?
windows	82.91% <100.00%> (+0.05%)	⬆️

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Impacted Files	Coverage Δ
...c/Polly.Core/Retry/RetryStrategyOptions.TResult.cs	100.00% <ø> (ø)
src/Polly.Core/Retry/RetryResilienceStrategy.cs	100.00% <100.00%> (ø)
.../Retry/RetryResilienceStrategyBuilderExtensions.cs	100.00% <100.00%> (ø)
src/Polly.Core/Strategy/EventInvoker.cs	100.00% <100.00%> (ø)
src/Polly.Core/Strategy/GeneratorInvoker.cs	100.00% <100.00%> (ø)
src/Polly.Core/Strategy/PredicateInvoker.cs	100.00% <100.00%> (ø)