Add fixture example in POM guide docs

[jfgreffier]

Using POM as a Playwright Test fixture is common, and fixtures are the way to go to set up tests. However the page https://playwright.dev/docs/pom has no example

• remove Playwright Test JavaScirpt examples, like the rest of docs
• add an example to add POM instance as fixture

[Skn0tt]

The removal of .js makes sense to me, but for the POM fixture we already have an example on the fixture page: https://playwright.dev/docs/test-fixtures#creating-a-fixture

Maybe we could link to that instead?

[jfgreffier]

The removal of .js makes sense to me, but for the POM fixture we already have an example on the fixture page: https://playwright.dev/docs/test-fixtures#creating-a-fixture

Maybe we could link to that instead?

OK, I made the change

[Skn0tt]

Reads good to me. cc @dgozman for final review