Introduce public API for Hedging Resilience Strategy

[martintmk]

The issue or feature being addressed

Contributes to #876

Details on the issue fix or feature implementation

This PR introduces the public API shape for the hedging strategy. The implementation of hedging strategy to be done in follow-up.

API usage:

// Generic hedging for handling of single result type
builder.AddHedging(new HedgingStrategyOptions<HttpResponseMessage>
{
    MaxHedgedAttempts = 3,
    HedgingDelay = TimeSpan.FromSeconds(3),
    ShouldHandle = new OutcomePredicate<HandleHedgingArguments, HttpResponseMessage>()
        .HandleResult(r => !r.IsSuccessStatusCode)
        .HandleException<HttpRequestException>(),
    HedgingActionGenerator = args =>
    {
        return async ()
        {
             HttpResponseMessage response = await CreateHedgedResponseAsync();
             return response;
        }
    }
});

// Non-generic hedging for handling of multiple result types
builder.AddHedging(new HedgingStrategyOptions
{
    MaxHedgedAttempts = 3,
    HedgingDelay = TimeSpan.FromSeconds(3),
    Handler = new HedgingHandler().SetHedging<HttpResponseMessage>(handler =>
    {
        handler.ShouldHandle
                .HandleResult(r => !r.IsSuccessStatusCode)
                .HandleException<HttpRequestException>();

        handler.HedgingActionGenerator = args =>
        {
            return async ()
            {
                 HttpResponseMessage response = await CreateHedgedResponseAsync();
                 return response;
            }
        };
    })
});

This API is very similar to one introduced for fallback strategy (#1158).

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 #1160 (8f04b74) into main (6cc8329) will increase coverage by 0.36%.
The diff coverage is 100.00%.

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@@            Coverage Diff             @@
##             main    #1160      +/-   ##
==========================================
+ Coverage   81.85%   82.21%   +0.36%     
==========================================
  Files         253      267      +14     
  Lines        5780     5898     +118     
  Branches      961      967       +6     
==========================================
+ Hits         4731     4849     +118     
  Misses        844      844              
  Partials      205      205              

Flag	Coverage Δ
linux	?
macos	82.21% <100.00%> (+0.36%)	⬆️
windows	82.21% <100.00%> (+0.36%)	⬆️

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

Impacted Files	Coverage Δ
src/Polly.Core/Fallback/FallbackHandler.Handler.cs	100.00% <ø> (ø)
src/Polly.Core/Fallback/FallbackHandler.TResult.cs	100.00% <ø> (ø)
src/Polly.Core/Fallback/FallbackHandler.cs	100.00% <ø> (ø)
src/Polly.Core/Fallback/VoidFallbackHandler.cs	100.00% <ø> (ø)
src/Polly.Core/Hedging/HandleHedgingArguments.cs	100.00% <100.00%> (ø)
...Hedging/HedgingActionGeneratorArguments.TResult.cs	100.00% <100.00%> (ø)
...ly.Core/Hedging/HedgingActionGeneratorArguments.cs	100.00% <100.00%> (ø)
src/Polly.Core/Hedging/HedgingConstants.cs	100.00% <100.00%> (ø)
src/Polly.Core/Hedging/HedgingDelayArguments.cs	100.00% <100.00%> (ø)
src/Polly.Core/Hedging/HedgingHandler.Handler.cs	100.00% <100.00%> (ø)
... and 9 more

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[martincostello]

Looks good. Could you add it to the benchmarks?

[martintmk]

Looks good. Could you add it to the benchmarks?

Yup, once the hedging strategy is implemented.