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

common/hugio/writers.go

@@ -81,3 +81,33 @@ func ToReadCloser(r io.Reader) io.ReadCloser {
 		io.NopCloser(nil),
 	}
 }
+
+type ReadWriteCloser interface {
+	io.Reader
+	io.Writer
+	io.Closer
+}
+
+// PipeReadWriteCloser is a convenience type to create a pipe with a ReadCloser and a WriteCloser.
+type PipeReadWriteCloser struct {
+	*io.PipeReader
+	*io.PipeWriter
+}
+
+// NewPipeReadWriteCloser creates a new PipeReadWriteCloser.
+func NewPipeReadWriteCloser() PipeReadWriteCloser {
+	pr, pw := io.Pipe()
+	return PipeReadWriteCloser{pr, pw}
+}
+
+func (c PipeReadWriteCloser) Close() (err error) {
+	if err = c.PipeReader.Close(); err != nil {
+		return
+	}
+	err = c.PipeWriter.Close()
+	return
+}
+
+func (c PipeReadWriteCloser) WriteString(s string) (int, error) {
+	return c.PipeWriter.Write([]byte(s))
+}