feature: new rules identical-switch-branches and identical-ifelseif-branches

These new rules result from the refactoring of `identical-branches` that will cover only simple/single if..else statements.

testdata/identical_switch_branches.go

@@ -0,0 +1,77 @@
+package fixtures
+
+func identicalSwitchBranches() {
+	switch a { // MATCH /"switch" with identical branches (lines 6 and 10)/
+	// expected values
+	case 1:
+		foo()
+	case 2:
+		bar()
+	case 3:
+		foo()
+	default:
+		return newError("blah")
+	}
+
+	// MATCH:18 /"switch" with identical branches (lines 20 and 24)/
+	// MATCH:18 /"switch" with identical branches (lines 22 and 26)/
+	switch a {
+	// expected values
+	case 1:
+		foo()
+	case 2:
+		bar()
+	case 3:
+		foo()
+	default:
+		bar()
+	}
+
+	switch a { // MATCH /"switch" with identical branches (lines 32 and 34)/
+	// expected values
+	case 1:
+		foo()
+	case 3:
+		foo()
+	default:
+
+	}
+
+	// Skip untagged switch
+	switch {
+	case a > b:
+		foo()
+	default:
+		foo()
+	}
+
+	// Do not warn on fallthrough
+
+	switch a {
+	case 1:
+		foo()
+		fallthrough
+	case 2:
+		fallthrough
+	case 3:
+		foo()
+	case 4:
+		fallthrough
+	default:
+		bar()
+	}
+
+	// skip type switch
+	switch v := value.(type) {
+	case int:
+		println("dup", v)
+	case string:
+		println("dup", v)
+	case bool:
+		println("dup", v)
+	case float64:
+		println("dup", v)
+	default:
+		println("dup", v)
+	}
+}