* validate file encoding

* add method to file rule helper

* test file rule helper

* add translation and replacements

* allow string or uploaded file

* generic message for strings and files

* handle invalid encoding parameter

* test more scenarios

* tidy grammar

* no @ silencing

* typo

* lowercase encodings

* doc block

* ci

* alpha

* test multiple

* generic test filenames

* formatting

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Co-authored-by: Taylor Otwell <taylor@laravel.com>