Hide validation APIs

[martintmk]

Details on the issue fix or feature implementation

Polly infra already validates all necessary options automatically. It was exposed only to validate TelemetryOptions but we can do it by linking internals.

If someone really needs it we can re-expose the API.

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 #1490 (d12ce7a) into main (72e5599) will not change coverage.
Report is 1 commits behind head on main.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main    #1490   +/-   ##
=======================================
  Coverage   83.71%   83.71%           
=======================================
  Files         272      272           
  Lines        6424     6424           
  Branches     1012     1012           
=======================================
  Hits         5378     5378           
  Misses        837      837           
  Partials      209      209           

Flag	Coverage Δ
linux	83.71% <100.00%> (ø)
macos	83.71% <100.00%> (ø)
windows	83.71% <100.00%> (ø)

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

Files Changed	Coverage Δ
src/Polly.Core/ResiliencePipelineBuilderBase.cs	100.00% <100.00%> (ø)
src/Polly.Core/ResilienceValidationContext.cs	100.00% <100.00%> (ø)
...ry/TelemetryResiliencePipelineBuilderExtensions.cs	100.00% <100.00%> (ø)