When using Perforce or PlasticSCM for version control, assets must be checked out for write access. The importer currently just goes and tries to overwrite file contents if the generated code has changed. This will fail if the asset is write-protected (IIRC Perforce indeed write-protects the files whereas PlasticSCM doesn't).

We need to communicate with the VCS integration to check out files, if needed.

May make sense to forego code-generation in this scenario. Something to consider.

Repro:
1. Create project and set up Perforce integration for it.
2. Create .inputactions asset, enable "Generate C# Class" for it and check it in.
3. Check out the .inputactions asset, edit it, and save it.

Result: the .inputactions asset importer will try to overwrite the .cs file and thus produce an error because the file is read-only.
Expected behavior: The importer should first check the file out using Unity version control APIs.

Also, try saving out the `.inputactions` asset without checking it out. This results in an exception.