fix(opencode): Use standard resolve function to get proper filePaths for tools

[OpeOginni]

Issue for this PR

Closes #18762

Type of change

• Bug fix
• New feature
• Refactor / code improvement
• Documentation

What does this PR do?

When setting permissions for tools in a project that does not have git initialised, it gets the paths of files relative to its worktree, and for non-git projects the worktree is always /, this breaks permissions as the filePath is not going to be what the Permission Rule expects.

So this PR adds a check if the worktree is / then go ahead to use the Instance directory. It also moves the resolve logic to its own file, so tools can all import from it, this makes the codebase a bit cleaner since all tools use the same logic.

How did you verify your code works?

I tested with the case the user had an issue with, for both a non-git project and a git project, it works as it should.

Also added regression tests to the tools affected. The fixes makes them all pass

Screenshots / recordings

Checklist

• I have tested my changes locally
• I have not included unrelated changes in this PR

[github-actions]

Thanks for your contribution!

This PR doesn't have a linked issue. All PRs must reference an existing issue.

Please:

1. Open an issue describing the bug/feature (if one doesn't exist)
2. Add Fixes #<number> or Closes #<number> to this PR description

See CONTRIBUTING.md for details.

[github-actions]

Thanks for updating your PR! It now meets our contributing guidelines. 👍