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/common.js

@@ -0,0 +1,56 @@
+// Read JSONL from stdin.
+export function readInput(handle) {
+	const buffSize = 1024;
+	let currentLine = [];
+	const buffer = new Uint8Array(buffSize);
+
+	// Read all the available bytes
+	while (true) {
+		// Stdin file descriptor
+		const fd = 0;
+		let bytesRead = 0;
+		try {
+			bytesRead = Javy.IO.readSync(fd, buffer);
+		} catch (e) {
+			// IO.readSync fails with os error 29 when stdin closes.
+			if (e.message.includes('os error 29')) {
+				break;
+			}
+			throw new Error('Error reading from stdin');
+		}
+
+		if (bytesRead < 0) {
+			throw new Error('Error reading from stdin');
+			break;
+		}
+
+		if (bytesRead === 0) {
+			break;
+		}
+
+		currentLine = [...currentLine, ...buffer.subarray(0, bytesRead)];
+
+		// Split array into chunks by newline.
+		let i = 0;
+		for (let j = 0; i < currentLine.length; i++) {
+			if (currentLine[i] === 10) {
+				const chunk = currentLine.splice(j, i + 1);
+				const arr = new Uint8Array(chunk);
+				const json = JSON.parse(new TextDecoder().decode(arr));
+				handle(json);
+				j = i + 1;
+			}
+		}
+		// Remove processed data.
+		currentLine = currentLine.slice(i);
+	}
+}
+
+// Write JSONL to stdout
+export function writeOutput(output) {
+	const encodedOutput = new TextEncoder().encode(JSON.stringify(output) + '\n');
+	const buffer = new Uint8Array(encodedOutput);
+	// Stdout file descriptor
+	const fd = 1;
+	Javy.IO.writeSync(fd, buffer);
+}