chore: removed circular dependency from BasicTracerProvider

[MingaudasVagonis]

Which problem is this PR solving?

Removing a circular dependency in opentelemetry-sdk-trace-base BasicTracerProvider.ts which was causing an error on React Native/Babel:
Cannot read property 'prototype' of undefined

Simply changed it to direct import, should not be an issue on other platforms.

Short description of the changes

Changed the import from '.' to './Tracer' and './SpanProcessor'.

Type of change

Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

How Has This Been Tested?

Retried getting a Tracer with the changes and the error was not there anymore, Tracer worked correctly.

Checklist:

• Followed the style guidelines of this project
• Unit tests have been added
• Documentation has been updated

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 94.67%. Comparing base (8ab52d5) to head (b951f06).
Report is 3 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5279      +/-   ##
==========================================
+ Coverage   94.66%   94.67%   +0.01%     
==========================================
  Files         322      322              
  Lines        8058     8058              
  Branches     1632     1632              
==========================================
+ Hits         7628     7629       +1     
+ Misses        430      429       -1     

Files with missing lines	Coverage Δ
...elemetry-sdk-trace-base/src/BasicTracerProvider.ts	95.68% <100.00%> (ø)

... and 1 file with indirect coverage changes