[Docs]: Upload Files documentation should document the __dirname alternative for ESM modules

### Page(s)

https://playwright.dev/docs/next/input#upload-files

### Description

The examples in the Upload Files sections use `__dirname` which exists only when using cjs modules.
When using ESM it should be replaced by `import.meta.dirname`.
See https://nodejs.org/api/esm.html#no-__filename-or-__dirname

The doc should either mention this or use relative paths.

