Add build time math rendering

While very useful on its own (and combined with the passthrough render hooks), this also serves as a proof of concept of using WASI (WebAssembly System Interface) modules in Hugo.

This will be marked _experimental_ in the documentation. Not because it will be removed or changed in a dramatic way, but we need to think a little more how to best set up/configure similar services, define where these WASM files gets stored, maybe we can allow user provided WASM files plugins via Hugo Modules mounts etc.

See these issues for more context:

* https://github.com/gohugoio/hugo/issues/12736
* https://github.com/gohugoio/hugo/issues/12737

See #11927

internal/warpc/gen/main.go

@@ -0,0 +1,55 @@
+//go:generate go run main.go
+package main
+
+import (
+	"fmt"
+	"log"
+	"os"
+	"path/filepath"
+	"strings"
+
+	"github.com/evanw/esbuild/pkg/api"
+)
+
+var scripts = []string{
+	"greet.js",
+	"renderkatex.js",
+}
+
+func main() {
+	for _, script := range scripts {
+		filename := filepath.Join("../js", script)
+		err := buildJSBundle(filename)
+		if err != nil {
+			log.Fatal(err)
+		}
+	}
+}
+
+func buildJSBundle(filename string) error {
+	minify := true
+	result := api.Build(
+		api.BuildOptions{
+			EntryPoints:       []string{filename},
+			Bundle:            true,
+			MinifyWhitespace:  minify,
+			MinifyIdentifiers: minify,
+			MinifySyntax:      minify,
+			Target:            api.ES2020,
+			Outfile:           strings.Replace(filename, ".js", ".bundle.js", 1),
+			SourceRoot:        "../js",
+		})
+
+	if len(result.Errors) > 0 {
+		return fmt.Errorf("build failed: %v", result.Errors)
+	}
+	if len(result.OutputFiles) != 1 {
+		return fmt.Errorf("expected 1 output file, got %d", len(result.OutputFiles))
+	}
+
+	of := result.OutputFiles[0]
+	if err := os.WriteFile(filepath.FromSlash(of.Path), of.Contents, 0o644); err != nil {
+		return fmt.Errorf("write file failed: %v", err)
+	}
+	return nil
+}