Cleanup Outcome internals and drop unused hedging and fallbacks APIs

[martintmk]

Details on the issue fix or feature implementation

Internal changes only.

• Drop non-generic APIs for fallback and hedging as there are not used nor exposed
• Simplify some hedging and fallback internals
• Cleanup Outcome<> struct.
  • The unsafe conversion between types moved to BridgeComponent as it is the only consumer
  • Conversion to and from Object-based outcomes dropped as it's no longer necessaary.

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 #1523 (37318c4) into main (94db492) will decrease coverage by 0.12%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main    #1523      +/-   ##
==========================================
- Coverage   84.11%   84.00%   -0.12%     
==========================================
  Files         278      278              
  Lines        6586     6540      -46     
  Branches     1026     1023       -3     
==========================================
- Hits         5540     5494      -46     
  Misses        837      837              
  Partials      209      209              

Flag	Coverage Δ
linux	84.00% <100.00%> (-0.12%)	⬇️
macos	84.00% <100.00%> (-0.12%)	⬇️
windows	84.00% <100.00%> (-0.12%)	⬇️

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

Files Changed	Coverage Δ
...rcuitBreakerResiliencePipelineBuilderExtensions.cs	100.00% <ø> (ø)
...Core/CircuitBreaker/CircuitBreakerStateProvider.cs	100.00% <ø> (ø)
...ack/FallbackResiliencePipelineBuilderExtensions.cs	100.00% <ø> (ø)
src/Polly.Core/Outcome.TResult.cs	100.00% <ø> (ø)
src/Polly.Core/Outcome.cs	100.00% <ø> (ø)
src/Polly.Core/Utils/TaskHelper.cs	100.00% <ø> (ø)
...CircuitBreaker/CircuitBreakerResilienceStrategy.cs	100.00% <100.00%> (ø)
...ircuitBreaker/Controller/CircuitStateController.cs	100.00% <100.00%> (ø)
src/Polly.Core/Fallback/FallbackHandler.cs	100.00% <100.00%> (ø)
.../Polly.Core/Fallback/FallbackResilienceStrategy.cs	100.00% <100.00%> (ø)
... and 6 more