js.Build: Generate tsconfig files

Updates #7777

Added support to allow SourceMap files to be external to the build.
In addition added more information when the js compilation has an error.
Correctly append sourceMappingURL to output file.
Fix merge conflict.

resources/resource_transformers/js/build_test.go

@@ -77,4 +77,20 @@ func TestToBuildOptions(t *testing.T) {
 		Sourcemap:         api.SourceMapInline,
 		Stdin:             &api.StdinOptions{},
 	})
+
+	opts, err = toBuildOptions(Options{
+		Target: "es2018", Format: "cjs", Minify: true, mediaType: media.JavascriptType,
+		SourceMap: "external"})
+	c.Assert(err, qt.IsNil)
+	c.Assert(opts, qt.DeepEquals, api.BuildOptions{
+		Bundle:            true,
+		Target:            api.ES2018,
+		Format:            api.FormatCommonJS,
+		MinifyIdentifiers: true,
+		MinifySyntax:      true,
+		MinifyWhitespace:  true,
+		Sourcemap:         api.SourceMapExternal,
+		Stdin:             &api.StdinOptions{},
+	})
+
 }