existence_requirement argument for FungibleLedger trait functions

[ghzlatarev]

Description

closes: #637

• Add existence_requirement enum argument to three of the functions in FungibleLedger trait: burn, can_withdraw, transfer
• For MantaPay cases KeepAlive is now used everywhere, whereas before some calls were with KeepAlive and others were AllowDeath
• For XCM cases AllowDeath is used, as was prior to this PR.
• Renamed can_withdraw to can_reduce_by_amount and removed all related error codes. There's only 1 error code now CannotReduceMoreThan(Balance)
• The reason for renaming was that it no longer uses fungible/s can_withdraw but reducible_amount because it accepts a keep_alive argument.
• In our burn function, which uses fungble/s burn_from the existence_requirement is checked in the can_reduce_by_amount prior to calling burn_from, which doesn't accept the existence_requirement argument, but uses AllowDeath internally. In the case of a user selecting KeepAlive the function can exit early.
• Added more integration tests to cover new cases.

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• If runtime changes, need to update the version numbers properly:
  • authoring_version: The version of the authorship interface. An authoring node will not attempt to author blocks unless this is equal to its native runtime.
  • spec_version: The version of the runtime specification. A full node will not attempt to use its native runtime in substitute for the on-chain Wasm runtime unless all of spec_name, spec_version, and authoring_version are the same between Wasm and native.
  • impl_version: The version of the implementation of the specification. Nodes are free to ignore this; it serves only as an indication that the code is different; as long as the other two versions are the same then while the actual code may be different, it is nonetheless required to do the same thing. Non-consensus-breaking optimizations are about the only changes that could be made which would result in only the impl_version changing.
  • transaction_version: The version of the extrinsics interface. This number must be updated in the following circumstances: extrinsic parameters (number, order, or types) have been changed; extrinsics or pallets have been removed; or the pallet order in the construct_runtime! macro or extrinsic order in a pallet has been changed. You can run the metadata_diff.yml workflow for help. If this number is updated, then the spec_version must also be updated
• Verify benchmarks & weights have been updated for any modified runtime logics
• If importing a new pallet, choose a proper module index for it, and allow it in BaseFilter. Ensure every extrinsic works from front-end. If there's corresponding tool, ensure both work for each other.
• If needed, update our Javascript/Typescript APIs. These APIs are officially used by exchanges or community developers.
• If modifying existing runtime storage items, make sure to implement storage migrations for the runtime and test them with try-runtime. This includes migrations inherited from upstream changes, and you can search the diffs for modifications of #[pallet::storage] items to check for any.

[Garandor]

A question, but the logic LGTM

[Dengjianping]

LGTM!

[Dengjianping]

LGTM!