Use invokers in fallback and hedging

[martintmk]

Details on the issue fix or feature implementation

Follow-up and finalization of #1229.

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 #1232 (3f5abb2) into main (7049574) will increase coverage by 0.01%.
The diff coverage is 100.00%.

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@@            Coverage Diff             @@
##             main    #1232      +/-   ##
==========================================
+ Coverage   82.92%   82.93%   +0.01%     
==========================================
  Files         267      267              
  Lines        6142     6148       +6     
  Branches      972      968       -4     
==========================================
+ Hits         5093     5099       +6     
  Misses        844      844              
  Partials      205      205              

Flag	Coverage Δ
linux	82.93% <100.00%> (+0.01%)	⬆️
macos	82.93% <100.00%> (+0.01%)	⬆️
windows	82.93% <100.00%> (+0.01%)	⬆️

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Impacted Files	Coverage Δ
...y.Core/Fallback/FallbackStrategyOptions.TResult.cs	100.00% <ø> (ø)
...lly.Core/Hedging/HedgingStrategyOptions.TResult.cs	100.00% <ø> (ø)
.../Polly.Core/Fallback/FallbackResilienceStrategy.cs	100.00% <100.00%> (ø)
...ack/FallbackResilienceStrategyBuilderExtensions.cs	100.00% <100.00%> (ø)
...rc/Polly.Core/Hedging/HedgingResilienceStrategy.cs	100.00% <100.00%> (ø)
...ging/HedgingResilienceStrategyBuilderExtensions.cs	100.00% <100.00%> (ø)