Fix: Don't use type aliases with external references

In the case that we're referencing a type defined in an external
package, using an alias here results in build errors i.e.:

  ./api.gen.go:93:7: cannot define new methods on non-local type common.TypeNameHere

Instead, we can make sure we only alias when there's not an external
reference in use, using the new `Schema.IsExternalRef` function.

pkg/codegen/templates/strict/strict-fiber-interface.tmpl

@@ -48,7 +48,7 @@
                 type {{$receiverTypeName}} struct{ {{$ref}}{{.NameTagOrContentType}}Response }
                 {{end}}
             {{else if and (not $hasHeaders) ($fixedStatusCode) (.IsSupported) -}}
-                type {{$receiverTypeName}} {{if eq .NameTag "Multipart"}}func(writer *multipart.Writer)error{{else if .IsSupported}}{{if .Schema.IsRef}}={{end}} {{.Schema.TypeDecl}}{{else}}io.Reader{{end}}
+                type {{$receiverTypeName}} {{if eq .NameTag "Multipart"}}func(writer *multipart.Writer)error{{else if .IsSupported}}{{if and .Schema.IsRef (not .Schema.IsExternalRef)}}={{end}} {{.Schema.TypeDecl}}{{else}}io.Reader{{end}}
             {{else -}}
                 type {{$receiverTypeName}} struct {
                     Body {{if eq .NameTag "Multipart"}}func(writer *multipart.Writer)error{{else if .IsSupported}}{{.Schema.TypeDecl}}{{else}}io.Reader{{end}}

pkg/codegen/templates/strict/strict-interface.tmpl

@@ -50,7 +50,7 @@
                 type {{$receiverTypeName}} struct{ {{$ref}}{{.NameTagOrContentType}}Response }
                 {{end}}
             {{else if and (not $hasHeaders) ($fixedStatusCode) (.IsSupported) -}}
-                type {{$receiverTypeName}} {{if eq .NameTag "Multipart"}}func(writer *multipart.Writer)error{{else if .IsSupported}}{{if .Schema.IsRef}}={{end}} {{.Schema.TypeDecl}}{{else}}io.Reader{{end}}
+                type {{$receiverTypeName}} {{if eq .NameTag "Multipart"}}func(writer *multipart.Writer)error{{else if .IsSupported}}{{if and .Schema.IsRef (not .Schema.IsExternalRef)}}={{end}} {{.Schema.TypeDecl}}{{else}}io.Reader{{end}}
             {{else -}}
                 type {{$receiverTypeName}} struct {
                     Body {{if eq .NameTag "Multipart"}}func(writer *multipart.Writer)error{{else if .IsSupported}}{{.Schema.TypeDecl}}{{else}}io.Reader{{end}}

pkg/codegen/templates/strict/strict-iris-interface.tmpl

@@ -50,7 +50,7 @@
                 type {{$receiverTypeName}} struct{ {{$ref}}{{.NameTagOrContentType}}Response }
                 {{end}}
             {{else if and (not $hasHeaders) ($fixedStatusCode) (.IsSupported) -}}
-                type {{$receiverTypeName}} {{if eq .NameTag "Multipart"}}func(writer *multipart.Writer)error{{else if .IsSupported}}{{if .Schema.IsRef}}={{end}} {{.Schema.TypeDecl}}{{else}}io.Reader{{end}}
+                type {{$receiverTypeName}} {{if eq .NameTag "Multipart"}}func(writer *multipart.Writer)error{{else if .IsSupported}}{{if and .Schema.IsRef (not .Schema.IsExternalRef)}}={{end}} {{.Schema.TypeDecl}}{{else}}io.Reader{{end}}
             {{else -}}
                 type {{$receiverTypeName}} struct {
                     Body {{if eq .NameTag "Multipart"}}func(writer *multipart.Writer)error{{else if .IsSupported}}{{.Schema.TypeDecl}}{{else}}io.Reader{{end}}