refactor!(chain): Unify ChangeSet nomenclature

refactor!(chain): Unify ChangeSet nomenclature

This commit renames:

- indexed_tx_graph::IndexedAdditions -> indexed_tx_graph::ChangeSet
- indexed_tx_graph::IndexedAdditions::graph_additions -> indexed_tx_graph::ChangeSet::graph
- indexed_tx_graph::IndexedAdditions::index_additions -> indexed_tx_graph::ChangeSet::indexer
- tx_graph::Additions -> tx_graph::ChangeSet
- keychain::DerivationAdditions -> keychain::ChangeSet
- CanonicalTx::node -> CanonicalTx::tx_node
- CanonicalTx::observed_as -> CanonicalTx::chain_position
- LocalChangeSet -> WalletChangeSet
- LocalChangeSet::chain_changeset -> WalletChangeSet::chain
- LocalChangeSet::indexed_additions -> WalletChangeSet::indexed_tx_graph
- LocalUpdate -> WalletUpdate

This commit also changes the visibility of TxGraph::determine_changeset
to be pub(crate), and the method accepts a TxGraph instead of &TxGraph

This commit removes:
- `TxGraph::insert_txout_preview`
- `TxGraph::insert_tx_preview`
- `insert_anchor_preview`
- `insert_seen_at_preview`

Solves #1022