improve mechanism for warnings in ui machines?

[janmazak]

There is a weakness in the design of the security policy return value mechanism. Originally, at most 1 warning was displayed, as the first step of the state machine. That is no longer true, but the return value does not convey the reason for warning, and the ui state machines have to be linear (because of how the macros are written), and now it is not possible to avoid displaying the warning just by skipping the first ui step. Not easy to improve.

In policyForSignTxInit, there are functions for warnings:

	WARN_IF(needsMissingCollateralWarning(txSigningMode, numCollateralInputs));
	WARN_IF(needsUnknownCollateralWarning(txSigningMode, numCollateralInputs));
	WARN_IF(needsMissingScriptDataHashWarning(txSigningMode, includeScriptDataHash));

relevant only for Plutus signing mode but called outside of the switch case.

Also,

		// Plutus script cannot be executed without script data hash
		WARN_UNLESS(includeScriptDataHash);

in the above switch duplicates needsMissingScriptDataHashWarning.