Murisi/multisig reordering

[murisi]

Describe your changes

Making the multisignature changes more compatible with hardware wallet signing. The core issue is that the final transaction building API settled upon needs to allow consumers to 1) build transactions 2) generate test vector 3) filter out sensitive sections 4) sign the transaction and 5) broadcast the transaction in that order. Some notes on the above ordering:

• Steps (3) and (4) may optionally happen on a hardware wallet which is able to parse only a Borsh serialized Tx object
• Step (2) must happen before step (3) because signing test vectors need to contain sensitive data to be useful
• Step (3) must happen before step (4) otherwise signatures over filtered out data will be rejected by protocol

The following changes have been made in order to achieve the above goal:

• Code reordered so that the following order is observed: build, generate test vector, filter, sign, broadcast
• The TxBuilder API has been merged into the Tx API and the build function has been removed
  • This way presigned prefiltered Txs will now be available to consumers.
• The add_gas_payer and add_signing_keys functions have been mutated into sign_wrapper and sign_raw.
• The builder API is now based on mutable references instead of ownership, in order to reduce the amount of moving

Indicate on which release or other PRs this topic is based on

Based on #1765 .

Checklist before merging to draft

• I have added a changelog
• Git history is in acceptable state

[tzemanovic]

I left couple smaller comments, besides that LGTM

[tzemanovic]

the cli params in tests/src/integration/masp.rs need to be updated for multisig (can run faster with #1768)