Migrate SigVerificationDecorator AnteHandler to use x/tx legacy amino json sign mode

[kocubinski]

Summary

Now that #15170 is completed we should migrate SigVerificationDecorator ante handler to use the new code.

Problem Definition

Once this is done we should be able to fully deprecate/break usages of GetSignBytes. This pattern is an obstacle to resolving cyclic module dependencies in x/auth and elsewhere. A global codec.LegacyAmino ref is initialized in an init() in modules. The sole reason for this seems to be the implementations of LegacyMsg.GetSignBytes, e.g. auth.MsgUpdateParams.

Implementing this will improve overall code quality (no globals) and move us closer to the longstanding goal of separating SDK modules into independent go modules - #11899.

Proposal

Integrate the legacy amino json sign mode in #15515 into SigVerificationDecorator.

Requires:

• x/tx transaction decoder #15411