chore(deps): Updated to Theia 1.39.0 (#2144)

- update Theia to `1.39.0`,
 - remove the application packager and fix the security vulnerabilities,
 - bundle the backed application with `webpack`, and
 - enhance the developer docs.

Co-authored-by: Akos Kitta <a.kitta@arduino.cc>
Co-authored-by: per1234 <accounts@perglass.com>

Signed-off-by: Akos Kitta <a.kitta@arduino.cc>

.eslintrc.js

@@ -15,7 +15,9 @@ module.exports = {
         '.browser_modules/*',
         'docs/*',
         'scripts/*',
-        'electron-app/*',
+        'electron-app/lib/*',
+        'electron-app/src-gen/*',
+        'electron-app/gen-webpack*.js',
         '!electron-app/webpack.config.js',
         'plugins/*',
         'arduino-ide-extension/src/node/cli-protocol',