Improve support for file changes detection when running UI mode in Docker

[edumserrano]

Problem

In some cases, when running on Docker, file change detection will not be available which means the target test app doesn't get rebuild when you change the code. This is problematic when running the UI mode via Docker.

The root cause comes down to:

In cases where Angular CLI is running in a shared directory on linux VM on a windows host the webpack dev server isn't detecting file changes from the host environment. (ex: Whenever a docker dev environment is running on a windows host.)
This is solved by adding poll option to the webpack dev server configuration. By default when no poll interval is set watchpack will use native file system change detection. This change allows for setting the poll interval which will turn on polling. ¹

Possible solutions

1. The simplest solution is to add the --poll option to the ng serve command executed by the playwright.config.ts. That's what is implemented by this PR.
2. Alternatively, when running Docker Desktop for Windows, switch to WSL1 instead of using WSL2.²
3. Lastly, you could run the target test app outside of Docker and then use the existing -useHostWebServer option:

   npm run test:ui '--' -useHostWebServer
   

   Since the app is running outside of Docker the file change detection will work as usual and the -useHostWebServer will make the tests running on Docker execute against the instance of the app running on the host

Changes

• added logic to automatically decide if the ng serve command requires the --poll flag.
• allow enforcing or not the --poll flag for the ng serve command .
• update documentation to reflect the new options as well as to describe the root cause behind the file changes not being detected in some scenarios.

Footnotes

1. feat(webpackDevServer): Add watchOptions for webpackDevServer #1814 ↩

2. Nodemon and webpack-dev-server hot reload not working under WSL 2 after Windows 10 resinstall ↩