templating: add resolvePath function for absolute path resolution

[SergioChan]

Summary

• add a new resolvePath template function to resolve relative segments into an absolute path
• make resolvePath resolve symlinks when available, with a safe fallback to the absolute path when symlink resolution is not possible
• add focused unit tests for path normalization and symlink resolution behavior

Testing

• Not run in this environment: go test ./internal/templater
• Reason: the repository requires Go 1.25 toolchain and this runtime cannot download/provision that toolchain (toolchain not available)

Related

• Fixes Add a resolvePath or absPath function #2681

[trulede]

Is more granular approach better?

absPath: filepath.Abs
evalSymlinks: filepathEvalSymlinks

[SergioChan]

Great question! I intentionally kept this as a single resolvePath helper because issue #2681 is about resolving template paths to a final usable absolute path, and exposing one focused function keeps the template surface smaller.

Current behavior is effectively:

1. filepath.Abs(...)
2. best-effort filepath.EvalSymlinks(...)
3. fallback to the absolute path if symlink evaluation fails

If you prefer explicit absPath and evalSymlinks helpers instead, I can split this PR that way.

[trulede]

The general approach has been to add individual functions. I think its more useful.