[BUILD] Need fine-grained HAVE_CPP_STDLIB

[marcalff]

Fixes #1071

Changes

Fixed the following issues with unit tests:

• In nostd/span_test.cc:

  • the unit tests were expecting specific behaviors when contructing a span with a static extent, and providing the wrong element count.
  • According to item (2) in https://en.cppreference.com/w/cpp/container/span/span, this is undefined behavior.
  • Resolved by removing tests that expected undefined behavior, as the result is implementation dependent anyway (the STL implementation was not tested because of possible differences).

• In url_parser_test:

  • The makefile with CMake did not depend on opentelemetry_api.
  • As a result, option WITH_STL was not honored per CMake settings, it was always unset
  • Fixed to always honor WITH_STL by adding the dependency on opentelemetry_api

Fixed namespace pollution in the API header files:

• #define HAVE_SPAN is replaced by #define OPENTELEMETRY_HAVE_SPAN
• #define HAVE_CPP_STDLIB is replaced by #define OPENTELEMETRY_STL_VERSION=<version>

Improved the granularity of the CMake WITH_STL option:

• Before, WITH_STL was either a "all" (C++20, or C++17 with extra code) or nothing choice.
• After, WITH_STL can gradually pick witch parts of the STL to use, with OFF, CXX11, CXX14, CXX17, CXX20 or CXX23 options.

Fixed compiling options pollution in CMake:

• Before, the makefile could decide to set CMAKE_CXX_STANDARD to specific values, possibly interfering with existing applications makefiles and compiling options.
• After, CMAKE_CXX_STANDARD is no longer overwritten. The CMAKE_CXX_STANDARD setting, if any, or the stdc++ compiler options, if any, provided by the caller are honored.

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

Merging #2304 (0c0b5c0) into main (5e96b80) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main    #2304   +/-   ##
=======================================
  Coverage   87.45%   87.45%           
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  Files         199      199           
  Lines        5997     5997           
=======================================
  Hits         5244     5244           
  Misses        753      753           

Files	Coverage Δ
api/include/opentelemetry/nostd/shared_ptr.h	100.00% <ø> (ø)
api/include/opentelemetry/nostd/span.h	90.00% <ø> (ø)
api/include/opentelemetry/nostd/string_view.h	97.96% <ø> (ø)
api/include/opentelemetry/nostd/unique_ptr.h	100.00% <ø> (ø)
api/include/opentelemetry/nostd/utility.h	83.34% <ø> (ø)
api/include/opentelemetry/nostd/variant.h	66.67% <ø> (ø)