Add interface alias support to cmg (#553)

* Add interface alias support to `cmg`

- Add support for making mocks for exported aliases that point to
  interface types in the `cmg` tool.

* Fix embedding generic interfaces

* Make lint happy

* Use cast with ok instead of type switch when type switch is not really needed

Author: douglaswth

mock/cmd/cmg/pkg/generate/_tests/extensive/aliased/imported.go

@@ -6,4 +6,8 @@ type (
 	Interface interface {
 		Imported(Type) Type
 	}
+
+	Generic[T any] interface {
+		ImportedGeneric(T) T
+	}
 )

mock/cmd/cmg/pkg/generate/_tests/extensive/extensive.go

@@ -43,15 +43,25 @@ type (
 
 		Embedded
 		imported.Interface
+
+		EmbeddedGeneric[uint16, uint32]
+		imported.Generic[rune]
 	}
 
 	Embedded interface {
 		Embedded(int8) int8
 	}
 
+	EmbeddedGeneric[X, Y any] interface {
+		EmbeddedGeneric(x X, y Y) (X, Y)
+	}
+
 	Generic[K comparable, V ~int | bool | string, X, Y any] interface {
 		Simple(k K, v V, x X, y Y) (K, V, X, Y)
 		Complex(map[K]V, []X, *Y, Set[K]) (map[K]V, []X, *Y, Set[K])
+
+		EmbeddedGeneric[X, Y]
+		imported.Generic[Y]
 	}
 
 	Struct                 struct{ A, B int }
@@ -62,4 +72,9 @@ type (
 	StructAlias            = struct{ A, B int }
 	IntSetAlias            = Set[int]
 	SetAlias[K comparable] = Set[K]
+
+	ExtensiveAlias                                               = Extensive
+	ImportedAlias                                                = imported.Interface
+	GenericAlias[K comparable, V ~int | bool | string, X, Y any] = Generic[K, V, X, Y]
+	ConstrainedGenericAlias                                      = Generic[string, IntAlias, float32, float64]
 )