@grafana/e2e: correctly exclude dependencies from TypeScript builds (#22732)

* maintains support for Grafana core e2e tests
* avoids producing declaration files in plugin source directories

packages/grafana-e2e/cypress/plugins/typescriptPreprocessor.js

+const { resolve } = require('path');
 const wp = require('@cypress/webpack-preprocessor');
 const wp = require('@cypress/webpack-preprocessor');
 
 
+const anyNodeModules = /node_modules/;
+const packageRoot = resolve(`${__dirname}/../../`);
+const packageModules = `${packageRoot}/node_modules`;
+
 const webpackOptions = {
 const webpackOptions = {
   module: {
   module: {
     rules: [
     rules: [
       {
       {
+        include: modulePath => {
+          if (!anyNodeModules.test(modulePath)) {
+            // Is a file within the project
+            return true;
+          } else {
+            // Is a file within this package
+            return modulePath.startsWith(packageRoot) && !modulePath.startsWith(packageModules);
+          }
+        },
         test: /\.ts$/,
         test: /\.ts$/,
         use: [
         use: [
           {
           {

packages/grafana-e2e/cypress/tsconfig.json

 {
 {
   "compilerOptions": {
   "compilerOptions": {
+    "declaration": false,
+    "module": "commonjs",
     "types": ["cypress"]
     "types": ["cypress"]
   },
   },
-  "extends": "../tsconfig.json",
+  "extends": "@grafana/tsconfig",
   "include": ["**/*.ts"]
   "include": ["**/*.ts"]
 }
 }