remove ImplicitUsings disable from projects (part 8)

[TimothyMothra]

Towards #3958.
Follow up to #3959.

In my previous PR, I enabled ImplicitUsings in Common.props and disabled this in projects with errors.
This PR fixes some projects and turns ImplicitUsings back on.

Changes

• remove #pragma warning disable IDE0005 introduced in previous PRs
• remove ImplicitUsings disable from projects
  • OpenTelemetry
  • OpenTelemetry.Api

Please provide a brief description of the changes here.

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

• Appropriate CHANGELOG.md updated for non-trivial changes
• Design discussion issue #
• Changes in public API reviewed

[codecov]

Codecov Report

Merging #3993 (69ec486) into main (ab3e407) will increase coverage by 85.56%.
The diff coverage is n/a.

Additional details and impacted files

@@            Coverage Diff            @@
##           main    #3993       +/-   ##
=========================================
+ Coverage      0   85.56%   +85.56%     
=========================================
  Files         0      288      +288     
  Lines         0    11070    +11070     
=========================================
+ Hits          0     9472     +9472     
- Misses        0     1598     +1598     

Impacted Files	Coverage Δ
src/OpenTelemetry.Api/Baggage.cs	100.00% <ø> (ø)
src/OpenTelemetry.Api/BaseProvider.cs	100.00% <ø> (ø)
...emetry.Api/Context/AsyncLocalRuntimeContextSlot.cs	75.00% <ø> (ø)
...nTelemetry.Api/Context/Propagation/B3Propagator.cs	85.86% <ø> (ø)
...metry.Api/Context/Propagation/BaggagePropagator.cs	85.48% <ø> (ø)
.../Context/Propagation/CompositeTextMapPropagator.cs	83.33% <ø> (ø)
...y.Api/Context/Propagation/NoopTextMapPropagator.cs	0.00% <ø> (ø)
...etry.Api/Context/Propagation/PropagationContext.cs	64.28% <ø> (ø)
....Api/Context/Propagation/TraceContextPropagator.cs	87.64% <ø> (ø)
...etry.Api/Context/Propagation/TraceStateUtilsNew.cs	83.00% <ø> (ø)
... and 395 more