Trace Exporter should respect noexcept qualifiers

[dbolduc]

These are virtual functions and we need to respect the specification.

I tried (and failed) to convince these folks to drop the noexcept.

It seems that we will need to capture all exceptions. Maybe something like this (

// in some header...
bool NoExceptAction(absl::FunctionRef<void()> action) noexcept;

// in some cc
#if GOOGLE_CLOUD_CPP_HAVE_EXCEPTIONS
bool NoExceptAction(absl::FunctionRef<void()> action) noexcept try {
  action();
  return true;
} catch(...) {
  return false;
}
#else
bool NoExceptAction(absl::FunctionRef<void()> action) noexcept {
  action(); // Will crash, would have crashed anyway.
  return true;
}
#endif

// In Recordable.cc
void Recordable::SetIdentity(...) {
  usable_ = usable_ & NoExceptAction([&]() { SetIdentityImpl(...); });
}

Then we will drop (not send to Cloud Trace) any Recordables where usable_ is false.

This is all for a TODO bug and future PRs.

Originally posted by @coryan in #11286 (comment)