rpc-v2/tx/tests: Add transaction broadcast tests and check propagated tx status (#3193)

This PR adds tests for the `transaction_broadcast` method.


The testing needs to coordinate the following components:
- The `TestApi` marks transactions as invalid and implements
`ChainApi::validate_transaction`
- this is what dictates if a transaction is valid or not and is called
from within the `BasicPool`
- The `BasicPool` which maintains the transactions and implements
`submit_and_watch` needed by the tx broadcast to submit the transaction
- The status of the transaction pool is exposed by mocking the BasicPool
- The `ChainHeadMockClient` which mocks the
`BlockchainEvents::import_notification_stream` needed by the tx
broadcast to know to which blocks the transaction is submitted

The following changes have been added to the substrate testing to
accommodate this:
- `TestApi` gets ` remove_invalid`, counterpart to `add_invalid` to
ensure an invalid transaction can become valid again; as well as a
priority setter for extrinsics
- `BasicPool` test constructor is extended with options for the
`PoolRotator`
- this mechanism is needed because transactions are banned for 30mins
(default) after they are declared invalid
  - testing bypasses this by providing a `Duration::ZERO`

### Testing Scenarios

- Capture the status of the transaction as it is normally broadcasted
- `transaction_stop` is valid while the transaction is in progress
- A future transaction is handled when the dependencies are completed
- Try to resubmit the transaction at a later block (currently invalid)
- An invalid transaction status is propagated; the transaction is marked
as temporarily banned; then the ban expires and transaction is
resubmitted
  
This builds on top of:
https://github.com/paritytech/polkadot-sdk/pull/3079
Part of: https://github.com/paritytech/polkadot-sdk/issues/3084

cc @paritytech/subxt-team

---------

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>
Co-authored-by: James Wilson <james@jsdw.me>