[Solaris-star]

Fixes #126929.

On Windows, retry extension-module loading with a long-path-compatible DLL path when the initial load fails because the path exceeds legacy limits.

The change also adds the required Windows NEWS entry.

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• Issue: 'ImportError: DLL load failed while importing xxxxxxx: The filename or extension is too long' with LongPathsEnabled #126929

[mkanat]

Thanks for this! I hit this bug through a bazel build of a Python project on Windows. A change very similar to this one fixes it for me. A few things I noticed:

1. is_unc is also true for paths that already start with \\?\ or \\.\, which become \\?\UNC\?\.... So when an extension at such a path fails to load for an ordinary reason, such as the wrong architecture, the error becomes "The network path was not found" instead of the real one. For example, you can see bazel-contrib/rules_python#4071 already passes \\?\ paths, so its users would see this.
2. Minor: Retrying only on ERROR_FILENAME_EXCED_RANGE (206) would leave any other error as it is today.
3. Minor: https://learn.microsoft.com/en-us/windows/win32/fileio/maximum-file-path-limitation says \\?\ paths are "passed to the system with minimal modification, which means that you cannot use forward slashes to represent path separators, or a period to represent the current directory, or double dots to represent the parent directory." GetFullPathNameW before adding the prefix would probably be safer.