Moved some functionality from Hub to Scope or Client:
- moved `add_breadcrumb` from Hub to Scope
- moved session functions from Hub to Scope
- moved `get_integration1` from Hub to Client.

This is preparation work for refactoring how we deal with Hubs and Scopes in the future.
Each commit is moving one function, so it should be easy to review commit by commit.

…)` (#2570)

Improves the capabilities of our threadlocal context variables, we use when no "real" context variables are available (for example in old Python versions)

- Adds a no-op [copy_context](https://docs.python.org/3/library/contextvars.html#contextvars.copy_context) function to use in environments without context vars
- Adds [reset](https://docs.python.org/3/library/contextvars.html#contextvars.ContextVar.reset) functionality to our threadlocal based context vars.

This is preparation work for refactoring how we deal with Hubs and Scopes in the future.

Moved some functionality from Hub to Client:

- Capture Event:
  - moved `capture_event` from Hub to Client
  - created new `capture_event` in Scope that calls `capture_event` in Client
  - made `capture_event` in Hub call the new `capture_event` in Scope

- Capture Exception:
  - created new `capture_exception` in Scope
  - made `capture_exception` in Hub call the new one in Scope

- Capture Message:
  - created new `capture_message` in Scope
  - made `capture_message` in Hub call the new one in Scope

- renamed `**scope_args` to `**scope_kwargs` because it contains keyword arguments.
- moved `_update_scope` from Hub to Scope and renamed it to `_merge_scopes` 

This is preparation work for refactoring how we deal with Hubs and Scopes in the future.
Its properly easier to reason about this change when checking out the branch than looking at the diff.

Moved some functionality from Hub to Client:

- sorted some typing imports
- moved `get_traceparent` from Hub to Scope
- moved `get_baggage` from Hub to Scope
- moved `iter_trace_propagation_headers` from Hub to Scope
- moved `trace_propagation_meta` from Hub to Scope

This is preparation work for refactoring how we deal with Hubs and Scopes in the future.

…on into new-scopes-add-api

…called from outside so they are not needed

Co-authored-by: Ivana Kellyerova <ivana.kellyerova@sentry.io>

…an have tests for it

Co-authored-by: Daniel Szoke <szokeasaurusrex@users.noreply.github.com>

…lity of the sdk here

Co-authored-by: Ivana Kellyerova <ivana.kellyerova@sentry.io>
Co-authored-by: Daniel Szoke <szokeasaurusrex@users.noreply.github.com>