What does this PR change? What problem does it solve?

restic currently uses ioutil.TempFile(...) to create its temporary files on Windows. As files cannot be deleted on Windows while these are still opened, restic sometimes leaves temporary files behind. This PR sets the FILE_FLAG_DELETE_ON_CLOSE flag to let windows delete the file automatically once all references were deleted. In addition, the flag FILE_ATTRIBUTE_TEMPORARY is added to avoid unnecessary writes of the temporary files to disk.

As os.Open and therefore ioutil.TempFile do not support these flags, this PR introduces a custom TempFile implementation, that directly calls syscall.CreateFile.

This PR is based on the code from @ducalex in #3465.

The temporary file is also created using shareMode 0, which prevents other processes from accessing the file in parallel. Thus restic is the only process which can open the file. As it will be deleted on close, this ensures that a tempfile can be removed, which fixes #1551.

Was the change previously discussed in an issue or on the forum?

Closes #3465.
Closes #1551.
Supersedes #3306.

Checklist

• I have read the contribution guidelines.
• I have enabled maintainer edits.
• I have added tests for all code changes.
• [ ] I have added documentation for relevant changes (in the manual).
• There's a new file in changelog/unreleased/ that describes the changes for our users (see template).
• I have run gofmt on the code in all commits.
• All commit messages are formatted in the same style as the other commits in the repo.
• I'm done! This pull request is ready for review.