[CONFIGURATION] Decouple SDK includes from builder interface classes

[dbarker]

Contributes to #4352

Follow up to #4335 to continue breaking dependencies between configuration_core and the SDK signal libraries.

The goal is to decouple the abstract builder headers from the SDK component headers. After this change, including an abstract builder header no longer pulls in the SDK headers of the component it builds. The SDK type is forward declared. The requirement for the complete type is deferred to the translation units that implement or invoke a builder, which by definition already include the concrete SDK header and link that signal's library.

This makes the contract for configuration_core more explicit in that it provides the
abstract builder headers without transitively providing the SDK signal headers.

Changes

• Replace SDK component includes with forward declarations in the abstract builder headers

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

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

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 80.86%. Comparing base (41cf715) to head (c9d84f1).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #4355   +/-   ##
=======================================
  Coverage   80.86%   80.86%           
=======================================
  Files         450      450           
  Lines       19216    19216           
=======================================
  Hits        15537    15537           
  Misses       3679     3679           

Files with missing lines	Coverage Δ
...figuration/extension_log_record_exporter_builder.h	100.00% <ø> (ø)
...iguration/extension_push_metric_exporter_builder.h	100.00% <ø> (ø)
...dk/configuration/extension_span_exporter_builder.h	100.00% <ø> (ø)
...sdk/configuration/periodic_metric_reader_builder.h	100.00% <ø> (ø)

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[marcalff]

LGTM