Moving extra declarations to npm module only

Tools/Gulp/config.json

@@ -1516,9 +1516,6 @@
                     "../../serializers/src/glTF/2.0/babylon.glTFData.ts",
                     "../../serializers/src/glTF/2.0/babylon.glTFMaterial.ts"
                 ],
-                "extraDeclarations": [
-                    "../../dist/babylon.glTF2Interface.d.ts"
-                ],
                 "output": "babylon.glTF2Serializer.js"
             }
         ],
@@ -1527,6 +1524,9 @@
             "distOutputDirectory": "/serializers/",
             "buildAsModule": true,
             "moduleName": "babylonjs-serializers",
+            "extraDeclarations": [
+                "../../dist/babylon.glTF2Interface.d.ts"
+            ],
             "outputFilename": "babylonjs.serializers",
             "moduleDeclaration": "BJSSerializers",
             "extendsRoot": true

Tools/Gulp/gulpfile.js

@@ -325,7 +325,9 @@ var buildExternalLibraries = function (settings) {
             let dtsFiles = files.map(function (filename) {
                 return filename.replace(".js", ".d.ts");
             });
-
+            if (settings.build.extraDeclarations) {
+                settings.build.extraDeclarations.forEach(file => { dtsFiles.unshift(file) })
+            }
             let dtsTask = gulp.src(dtsFiles)
                 .pipe(concat(settings.build.outputFilename + ".module.d.ts"))
                 .pipe(replace(referenceSearchRegex, ""))
@@ -405,14 +407,9 @@ var buildExternalLibrary = function (library, settings, watch) {
             .pipe(gulp.dest(outputDirectory));
         /*}*/
 
-        let preDts;
-        if (library.extraDeclarations) {
-            preDts = merge2([tsProcess.dts, gulp.src(library.extraDeclarations)])
-        } else {
-            preDts = tsProcess.dts;
-        }
 
-        var dts = preDts
+
+        var dts = tsProcess.dts
             .pipe(concat(library.output))
             .pipe(replace(referenceSearchRegex, ""))
             .pipe(rename({ extname: ".d.ts" }))