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