denominated units for balances in events

[SkymanOne]

Closes #673

Example of denomination of balances when running a call on substrate contracts node:

       Event Balances ➜ Transfer
         from: 5GrwvaEF5zXb26Fz9rcQpDWS57CtERHpNehXCPcNoHGKutQY
         to: 5FUdyfmrdbk1H5F1E4HnweiQjENqwAWnPxH2Mkty6LeK5at9
         amount: 100.2nDOT
       Event Balances ➜ Reserved
         who: 5FUdyfmrdbk1H5F1E4HnweiQjENqwAWnPxH2Mkty6LeK5at9
         amount: 100.2nDOT
       Event Balances ➜ Deposit
         who: 5GrwvaEF5zXb26Fz9rcQpDWS57CtERHpNehXCPcNoHGKutQY
         amount: 188.457902μDOT
       Event TransactionPayment ➜ TransactionFeePaid
         who: 5GrwvaEF5zXb26Fz9rcQpDWS57CtERHpNehXCPcNoHGKutQY
         actual_fee: 4.23927238nDOT
         tip: 0DOT

Update

Balances can also be inputed in a denominated format (i.e. 500MDOT for 500 x 10^6 x 10^<tokenDecimals>DOT).
The token symbol must match the one specified in the running local chain. If the chain config does not have a token symbol and/or decimals. UNIT is used as a default symbol and 12 decimals are used for denomination

This includes:

• --value for call and instantiate commands
• --storage_deposit_limit for any command

Includes fixes addressed in #751

[SkymanOne]

Currently blocked by #654 in subxt repo

[SkymanOne]

Updated documentation will follow after the approval from code owners

[ascjones]

The main thing is the code in balance.rs needs to be tightened up a bit, needs more tests since there are bugs there.

Also I think we are missing decoding Balance for contract events, for that the decode_contract_event would need to check for fields with the type name Balance: https://github.com/paritytech/cargo-contract/blob/05494e2bd62b48c6b79b99bd91c0657ee8656103/crates/transcode/src/lib.rs#L250

[ascjones]

The handling of the decimal parsing is much better now 👍

The conversion from raw u128 to DenominatedBalance needs some testing and tidying up.

One big thing that looks to be missing is the handling of Balance values when actually interacting with contracts. We should be able to use a denominated balance when invoking e.g. https://github.com/paritytech/ink/blob/master/examples/erc20/lib.rs#L130.

And also when displaying the resulting contract Transfer event: https://github.com/paritytech/ink/blob/master/examples/erc20/lib.rs#L27.

This needs to be done in https://github.com/paritytech/cargo-contract/blob/05494e2bd62b48c6b79b99bd91c0657ee8656103/crates/transcode/src/lib.rs#L250

[ascjones]

BalanceVariant::from still needs some tidying up.

For some inspiration, have a look at formatBalance that polkadot.js uses. It does so in a fairly concise manner. See e.g. calcSi

[ascjones]

LGTM