refactor (rule/receiver-naming): replace AST walker by iteration over declarations

[chavacava]

Simplifies receiver-naming rule by replacing AST walker by an iteration over global declarations

[ccoVeille]

You could use a switch

You are checking the same variable three times, also it would allow to remove the two continue, as they will be useless

Suggested change

	if name == "_" {
	failures = append(failures, lint.Failure{
	Node: decl,
	Confidence: 1,
	Category: "naming",
	Failure: "receiver name should not be an underscore, omit the name if it is unused",
	})
	continue
	}
	if name == "this" || name == "self" {
	failures = append(failures, lint.Failure{
	Node: decl,
	Confidence: 1,
	Category: "naming",
	Failure: `receiver name should be a reflection of its identity; don't use generic names such as "this" or "self"`,
	})
	continue
	}
	switch name {
	case "_":
	failures = append(failures, lint.Failure{
	Node: decl,
	Confidence: 1,
	Category: "naming",
	Failure: "receiver name should not be an underscore, omit the name if it is unused",
	})
	case "this", "self":
	failures = append(failures, lint.Failure{
	Node: decl,
	Confidence: 1,
	Category: "naming",
	Failure: `receiver name should be a reflection of its identity; don't use generic names such as "this" or "self"`,
	})
	}

[chavacava]

The switch on name will cope with the first two conditions for failure, the other conditions are not just on name thus IMO, adding a switch will not help in clarity (further, even with a switch continue is needed after adding a failure to do not evaluate the not-in-the-switch conditions)