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/js/greet.js

@@ -0,0 +1,9 @@
+import { readInput, writeOutput } from './common';
+
+const greet = function (input) {
+	writeOutput({ header: input.header, data: { greeting: 'Hello ' + input.data.name + '!' } });
+};
+
+console.log('Greet module loaded');
+
+readInput(greet);