Enable the ESLint no-debugger and no-alert rules

The `debugger`-statement would only, potentially, make sense during development and we thus want to prevent it from being accidentally included when landing code.
The `alert`, `confirm`, and `prompt` functions should generally be avoided, with the few intended cases manually allowed.

Please find additional details about the ESLint rules at:
 - https://eslint.org/docs/rules/no-debugger
 - https://eslint.org/docs/rules/no-alert

.eslintrc

@@ -45,6 +45,7 @@
     "no-async-promise-executor": "error",
     "no-cond-assign": ["error", "except-parens"],
     "no-constant-condition": ["error", { "checkLoops": false, }],
+    "no-debugger": "error",
     "no-dupe-args": "error",
     "no-dupe-else-if": "error",
     "no-dupe-keys": "error",
@@ -79,6 +80,7 @@
     "dot-notation": "error",
     "eqeqeq": ["error", "always"],
     "grouped-accessor-pairs": ["error", "getBeforeSet"],
+    "no-alert": "error",
     "no-caller": "error",
     "no-else-return": "error",
     "no-empty-pattern": "error",

examples/.eslintrc

@@ -19,6 +19,7 @@
   },
 
   "rules": {
+    "no-alert": "off",
     "object-shorthand": ["error", "never"]
   }
 }

web/app.js

@@ -1667,6 +1667,7 @@ const PDFViewerApplication = {
           "Warning: The PDF is not fully loaded for printing."
         )
         .then(notReadyMessage => {
+          // eslint-disable-next-line no-alert
           window.alert(notReadyMessage);
         });
       return;

web/chromecom.js

@@ -219,6 +219,7 @@ function requestAccessToLocalFile(fileUrl, overlayManager, callback) {
             "\nSelected: " +
             file.name +
             "\nDo you want to open the selected file?";
+          // eslint-disable-next-line no-alert
           if (!confirm(msg)) {
             this.value = "";
             return;