Change filePath to real path if it's an upload

[isaacdew2]

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1️⃣ Why should it be added? What are the benefits of this change?
The current state breaks cases where the UploadedFile is not on a local disk such as S3. I discovered this issue in a project when using S3 for Livewire temporary files. Currently, one must do $myImport->import($uploadedFile->getRealPath()) instead of $myImport->import($uploadedFile) when using S3 for temporary files.

2️⃣ Does it contain multiple, unrelated changes? Please separate the PRs out.
No.

3️⃣ Does it include tests, if possible?
No. I'm not sure how to add tests for this without a remote disk connection. If there's a way let me know!

4️⃣ Any drawbacks? Possible breaking changes?
There shouldn't be. It's a small change and for local UploadFile instances it should work exactly as it did before.

5️⃣ Mark the following tasks as done:

• Checked the codebase to ensure that your feature doesn't already exist.
• Take note of the contributing guidelines.
• Checked the pull requests to ensure that another person hasn't already submitted a fix.
• Added tests to ensure against regression.

6️⃣ Thanks for contributing! 🙌
Thank you for building an awesome package!