Do not send empty Route Change Transactions

[krystofwoldrich]

Description

In rare cases the SDK can send empty transaction named Route Change.

Actual

This happens when the navigation library API emits route change event but the current route api returns undefined.

Since route is undefined the SDK names the transaction Route Change, if no other auto instrumentation emits spans, the transaction will be empty.

Expected

The SDK should discard such a transaction as it doesn't contain any useful information. The SDK should record a dropped transaction, so we can observe frequency of this situation.

[krystofwoldrich]

The dropped tx should not show in reason sample_rate. Either in a new category or existing fitting one.