Drop TimeProvider.CancelAfter

[martintmk]

Details on the issue fix or feature implementation

In this PR we are syncing our internal implementation of time provider with the official one. In follow-up I'll try to address the Delay.

Contributes to #1348

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 #1352 (52b3b11) into main (761d969) will decrease coverage by 0.09%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main    #1352      +/-   ##
==========================================
- Coverage   83.59%   83.51%   -0.09%     
==========================================
  Files         270      268       -2     
  Lines        6396     6362      -34     
  Branches     1008      999       -9     
==========================================
- Hits         5347     5313      -34     
  Misses        840      840              
  Partials      209      209              

Flag	Coverage Δ
linux	83.51% <100.00%> (-0.09%)	⬇️
macos	83.51% <100.00%> (-0.09%)	⬇️
windows	83.51% <100.00%> (-0.09%)	⬇️

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

Impacted Files	Coverage Δ
...rc/Polly.Core/Utils/CancellationTokenSourcePool.cs	100.00% <ø> (ø)
...re/Utils/CancellationTokenSourcePool.Disposable.cs	100.00% <100.00%> (ø)
...y.Core/Utils/CancellationTokenSourcePool.Pooled.cs	100.00% <100.00%> (ø)

... and 5 files with indirect coverage changes