CopyMappingsDown applies mappings to implicit params

[Machine-Maker]

The CopyMappingsDown mappings change contributor doesn't check to make sure the parameter for which it is applying mappings would actually have a mapping.

class ParentClass {
	static class InnerStaticClass {
		InnerStaticClass(ParentClass parent, double value) {
		}
	}
}

class ChildClass extends ParentClass {
	class InnerClass extends ParentClass.InnerStaticClass {
		InnerClass(double value) {
			super(ChildClass.this, value);
		}
	}
}

The above example, if provided with mappings only for ParentClass$InnerStaticClass#<init> would apply 2 parameter mappings to ChildClass$InnerClass#<init>, the double param's mappings as well as the implicit ParentClass parameter.

I assume this is also an issue for any captured variables that would be in the constructor of a method-local class.

Tests I wrote to demo the issue: https://pastes.dev/BMugODf0zE