Update ExemplarFilter and ExemplarReservoir for spec

[ThomsonTan]

Fixes # (issue)

Changes

Please provide a brief description of the changes here.

For significant contributions please make sure you have completed the following items:

• [x] CHANGELOG.md updated for non-trivial changes
• [x] Unit tests have been added
• [ ] Changes in public API reviewed

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 0% with 5 lines in your changes are missing coverage. Please review.

Project coverage is 87.35%. Comparing base (497eaf4) to head (a9c4e76). Report is 56 commits behind head on main.

:exclamation: Current head a9c4e76 differs from pull request most recent head 8231e1e. Consider uploading reports for the commit 8231e1e to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2372      +/-   ##
==========================================
+ Coverage   87.12%   87.35%   +0.24%     
==========================================
  Files         200      199       -1     
  Lines        6109     6023      -86     
==========================================
- Hits         5322     5261      -61     
+ Misses        787      762      -25     

Files	Coverage Δ
sdk/src/metrics/meter_provider.cc	82.50% <0.00%> (-4.34%)	:arrow_down:
sdk/src/metrics/meter_context.cc	73.69% <0.00%> (-3.02%)	:arrow_down:

... and 36 files with indirect coverage changes

[marcalff]

Needs to be re evaluated after:

• https://github.com/open-telemetry/opentelemetry-specification/pull/3820

[ThomsonTan]

Talked with Lalit. He is fine to merge this PR and address potential feedback in future PRs.

I am going to merge it for now.