public void setExisting(Instruction existing) {
		this.existing = existing;
	}
Set the "existing" instruction used for ordering proposed instructions by "most similar"

@see #computePreference(AssemblyResolvedPatterns)
@param existing the existing instruction
Ghidra/Features/Base/src/main/java/ghidra/app/plugin/core/assembler/AssemblyDualTextField.java