Fix definitions for bad_variant_access and dependencies of some examples.

[owent]

Signed-off-by: owent admin@owent.net

Fixes #849

Changes

• Move CORE_RUNTIME_LIBS into dependency of opentelemetry_api

  I found all targets link CORE_RUNTIME_LIBS alse depend opentelemetry_api. So I move CORE_RUNTIME_LIBS into dependency of opentelemetry_api for easier usage.

• Add alias of nostd::bad_variant_access to absl::bad_variant_access when have abseil

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 #850 (6b0c1b8) into main (865b9e7) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main     #850   +/-   ##
=======================================
  Coverage   95.48%   95.48%           
=======================================
  Files         156      156           
  Lines        6615     6615           
=======================================
  Hits         6316     6316           
  Misses        299      299           

Impacted Files	Coverage Δ
api/include/opentelemetry/nostd/variant.h	66.67% <ø> (ø)

[lalitb]

Thank you for the fix. I will add CI for ABSIEL.

[lalitb]

@owent - will merge it once you rebase the changes.thanks.

[owent]

@owent - will merge it once you rebase the changes.thanks.

Done.