Add entryPointBaseUrl support for web workers

Introduces the entryPointBaseUrl property to configuration in index.html and flutter_bootstrap.js, and updates python.js to use this base URL when creating Python web workers. This change allows for more flexible deployment scenarios where the entry point base URL may differ.

{{cookiecutter.out_dir}}/web/flutter_bootstrap.js

@@ -3,6 +3,7 @@
 
 var flutterConfig = {
     multiViewEnabled: flet.multiView,
+    entryPointBaseUrl: flet.entryPointBaseUrl,
     assetBase: flet.assetBase
 };
 if (flet.webRenderer != "auto") {

{{cookiecutter.out_dir}}/web/index.html

@@ -25,6 +25,7 @@
       multiView: false,
       noCdn: "{{ cookiecutter.no_cdn }}".toLowerCase() == "true",
       webSocketEndpoint: "/ws",
+      entryPointBaseUrl: "/",
       assetBase: "/",
       routeUrlStrategy: "{{ cookiecutter.route_url_strategy }}",
       canvasKitBaseUrl: "/canvaskit/",

{{cookiecutter.out_dir}}/web/python.js

@@ -12,7 +12,8 @@ globalThis.jsConnect = async function(appId, args, dartOnMessage) {
     };
     console.log(`Starting up Python worker: ${appId}, args: ${args}`);
     _apps[appId] = app;
-    app.worker = new Worker("python-worker.js");
+    app.worker = new Worker((flet.entryPointBaseUrl.endsWith("/") ?
+        flet.entryPointBaseUrl.slice(0, -1) : flet.entryPointBaseUrl) + "python-worker.js");
 
     var error;
     app.worker.onmessage = (event) => {