accounts/abi: ABI explicit difference between Unpack and UnpackIntoInterface (#21091)

* accounts/abi: refactored abi.Unpack

* accounts/abi/bind: fixed error

* accounts/abi/bind: modified template

* accounts/abi/bind: added ToStruct for conversion

* accounts/abi: reenabled tests

* accounts/abi: fixed tests

* accounts/abi: fixed tests for packing/unpacking

* accounts/abi: fixed tests

* accounts/abi: added more logic to ToStruct

* accounts/abi/bind: fixed template

* accounts/abi/bind: fixed ToStruct conversion

* accounts/abi/: removed unused code

* accounts/abi: updated template

* accounts/abi: refactored unused code

* contracts/checkpointoracle: updated contracts to sol ^0.6.0

* accounts/abi: refactored reflection logic

* accounts/abi: less code duplication in Unpack*

* accounts/abi: fixed rebasing bug

* fix a few typos in comments

* rebase on master

Co-authored-by: Guillaume Ballet <gballet@gmail.com>