Implement handling of deposit-values in SCORU

This MR addresses issue #2449 (closed). The following changes have been made:

• freeze deposits in [Sc_rollup_storage.deposit_stake]
• unfreeze deposits in [Sc_rollup_storage.withdraw_stake]
• burn deposits in [Sc_rollup_storage.remove_staker]
• test that corresponding account balances change (or do not) as expected in existing tests
• update operations receipts to include balance updates generated by the freezing/unfreezing/burning of deposits

Manually testing the MR

CI, in particular :

dune exec src/proto_alpha/lib_protocol/test/unit/main.exe -- test "^\[Unit\] Sc_rollup_storage.ml$"