Code flagged noexcept should not raise exceptions

Currently, many APIs are flagged as noexcept.

For example:

class OPENTELEMETRY_EXPORT TracerProvider
{
public:
  virtual nostd::shared_ptr<Tracer> GetTracer(
      nostd::string_view name,
      nostd::string_view version,
      nostd::string_view schema_url,
      const common::KeyValueIterable *attributes) noexcept = 0;

When implemented in the SDK:

nostd::shared_ptr<trace_api::Tracer> TracerProvider::GetTracer(
    nostd::string_view name,
    nostd::string_view version,
    nostd::string_view schema_url,
    const opentelemetry::common::KeyValueIterable *attributes) noexcept
{
...
  auto tracer = std::shared_ptr<Tracer>(new Tracer(context_, std::move(scope)));
  tracers_.push_back(tracer);
  return nostd::shared_ptr<trace_api::Tracer>{tracer};
}

The call to new Tracer() can fail with bad_alloc, so an exception is still raised, breaking the noexcept contract.

Proposal:

nostd::shared_ptr<trace_api::Tracer> TracerProvider::GetTracerImpl(
    nostd::string_view name,
    nostd::string_view version,
    nostd::string_view schema_url,
    const opentelemetry::common::KeyValueIterable *attributes) {
}

nostd::shared_ptr<trace_api::Tracer> TracerProvider::GetTracer(
    nostd::string_view name,
    nostd::string_view version,
    nostd::string_view schema_url,
    const opentelemetry::common::KeyValueIterable *attributes) noexcept
{
  try {
    // invoke GetTracerImpl
  }
  catch {
    return a pre allocated Noop tracer instead.
  }
}

Forcing down the noexcept to the entire code base is not realistic, entry points to the SDK surface needs to handle failures explicitly instead, to give room to the SDK implementation to fail internally with exceptions if needed.

Start with TracerProvider::GetTracer and compare its noexcept API declaration with the SDK implementation shown in the issue. Trace other SDK surface entry points with the same contract, then define how failures and the pre-allocated Noop tracer should be handled; done means the affected entry points preserve noexcept without allowing allocation exceptions to escape.