livereload: Improve the livereload script build and update to v4.0.2

This script has very infrequent updates, but just copy pasting the minified source creates some potential trust issues.

This JS will now be pulled from a Git version and both the unminified and minified version gets written to disk.

This way it should be easier to reason about changes in the future.

To upgrade, change the commit hash and run `mage generate`.

Closes #12451
Closes #6290

livereload/gen/main.go

@@ -0,0 +1,61 @@
+//go:generate go run main.go
+package main
+
+import (
+	_ "embed"
+	"fmt"
+	"io"
+	"log"
+	"net/http"
+	"os"
+
+	"github.com/evanw/esbuild/pkg/api"
+)
+
+//go:embed livereload-hugo-plugin.js
+var livereloadHugoPluginJS string
+
+func main() {
+	// 4.0.2
+	// To upgrade to a new version, change to the commit hash of the version you want to upgrade to
+	// then run mage generate from the root.
+	const liveReloadCommit = "d803a41804d2d71e0814c4e9e3233e78991024d9"
+	liveReloadSourceURL := fmt.Sprintf("https://raw.githubusercontent.com/livereload/livereload-js/%s/dist/livereload.js", liveReloadCommit)
+
+	func() {
+		resp, err := http.Get(liveReloadSourceURL)
+		must(err)
+		defer resp.Body.Close()
+
+		b, err := io.ReadAll(resp.Body)
+		must(err)
+
+		// Write the unminified livereload.js file.
+		err = os.WriteFile("../livereload.js", b, 0o644)
+		must(err)
+
+		// Bundle and minify with ESBuild.
+		result := api.Build(api.BuildOptions{
+			Stdin: &api.StdinOptions{
+				Contents: string(b) + livereloadHugoPluginJS,
+			},
+			Outfile:           "../livereload.min.js",
+			Bundle:            true,
+			Target:            api.ES2015,
+			Write:             true,
+			MinifyWhitespace:  true,
+			MinifyIdentifiers: true,
+			MinifySyntax:      true,
+		})
+
+		if len(result.Errors) > 0 {
+			log.Fatal(result.Errors)
+		}
+	}()
+}
+
+func must(err error) {
+	if err != nil {
+		log.Fatal(err)
+	}
+}