gh-127111: Emscripten Make web example work again (#127113)

Moves the Emscripten web example into a standalone folder, and updates 
Makefile targets to build the web example. Instructions for usage have
also been added.

Tools/wasm/python.worker.js

@@ -1,87 +0,0 @@
-class StdinBuffer {
-    constructor() {
-        this.sab = new SharedArrayBuffer(128 * Int32Array.BYTES_PER_ELEMENT)
-        this.buffer = new Int32Array(this.sab)
-        this.readIndex = 1;
-        this.numberOfCharacters = 0;
-        this.sentNull = true
-    }
-
-    prompt() {
-        this.readIndex = 1
-        Atomics.store(this.buffer, 0, -1)
-        postMessage({
-            type: 'stdin',
-            buffer: this.sab
-        })
-        Atomics.wait(this.buffer, 0, -1)
-        this.numberOfCharacters = this.buffer[0]
-    }
-
-    stdin = () => {
-        while (this.numberOfCharacters + 1 === this.readIndex) {
-            if (!this.sentNull) {
-                // Must return null once to indicate we're done for now.
-                this.sentNull = true
-                return null
-            }
-            this.sentNull = false
-            // Prompt will reset this.readIndex to 1
-            this.prompt()
-        }
-        const char = this.buffer[this.readIndex]
-        this.readIndex += 1
-        return char
-    }
-}
-
-const stdout = (charCode) => {
-    if (charCode) {
-        postMessage({
-            type: 'stdout',
-            stdout: charCode,
-        })
-    } else {
-        console.log(typeof charCode, charCode)
-    }
-}
-
-const stderr = (charCode) => {
-    if (charCode) {
-        postMessage({
-            type: 'stderr',
-            stderr: charCode,
-        })
-    } else {
-        console.log(typeof charCode, charCode)
-    }
-}
-
-const stdinBuffer = new StdinBuffer()
-
-var Module = {
-    noInitialRun: true,
-    stdin: stdinBuffer.stdin,
-    stdout: stdout,
-    stderr: stderr,
-    onRuntimeInitialized: () => {
-        postMessage({type: 'ready', stdinBuffer: stdinBuffer.sab})
-    }
-}
-
-onmessage = (event) => {
-    if (event.data.type === 'run') {
-        if (event.data.files) {
-            for (const [filename, contents] of Object.entries(event.data.files)) {
-                Module.FS.writeFile(filename, contents)
-            }
-        }
-        const ret = callMain(event.data.args)
-        postMessage({
-            type: 'finished',
-            returnCode: ret
-        })
-    }
-}
-
-importScripts('python.js')