This PR makes the ASGI integration work both in legacy and span streaming mode. Some features and attributes will be missing in span streaming mode for now (see the Out of scope section below).

Best reviewed with whitespace ignored: https://github.com/getsentry/sentry-python/pull/5680/changes?w=1

A bit of a background on migrating integrations to span first. In order to support both legacy spans and span streaming, most integrations will follow the same patterns:

API

We need to use the start_span API from sentry_sdk.traces if we're in span streaming mode (traces_lifecycle="stream").

There are no transactions anymore. Top-level spans will also be started via the start_span API in span streaming mode.

Setting data on spans

If an integration sets data on a span (via span.set_data, span.set_tag etc.), it should use span.set_attribute when span streaming is enabled.

The attributes that we set need to be in Sentry conventions. This is deliberately not the case for most quick ports of integrations like this one and will follow in a future step.

Trace propagation

If an integration sits at a service boundary and is capable of propagating incoming trace information (like WSGI/ASGI or Celery), in span first mode we need to switch from the old style with continue_trace(...) as transaction: to the new style continue_trace() and new_trace() (not context managers).

start_span arguments

You can pass things like op, origin, source to the old start_span API. With the new API, this is no longer possible, and the individual properties need to be set as attributes directly.

Out of scope

For now, the following is out of scope and will follow in the future:

• Making sure all attributes are correct and that they're set in Sentry conventions: Migrate data, contexts, tags, event_processors to attributes #5152
• Migrating event processors (as streaming spans are not events, event processors are not run on them, meaning some data will not be set yet): Migrate data, contexts, tags, event_processors to attributes #5152