Fix cpp-lib example: dedupe react-native-windows in Metro config

[anuagragith]

Problem

The NativeModuleSample/cpp-lib example renders a blank screen at runtime. The
red box (with JS debugging / dev bundle) reveals:

Render Error: View config getter callback for component CircleMask must be a
function (received undefined).

This matches open issue microsoft/react-native-windows#15519 and reproduces on both 0.84 and 0.85.

Root cause

The example's metro.config.js loads two copies of react-native-windows — one
from the library root's node_modules and one from example/node_modules. Each copy
has its own ReactNativeViewConfigRegistry. codegenNativeComponent('CircleMask')
registers the view config into one instance, while the renderer looks it up in the
other → undefined → React throws → the whole tree unmounts (blank window).

The existing dedupe logic was a no-op because it:

1. Used the deprecated blacklistRE key (Metro 0.84 / RN 0.85 uses blockList).
2. Built patterns with Windows backslashes, which never match Metro's
   forward-slash-normalized module paths.

Fix

• Rename blacklistRE → blockList and normalize path separators so the root
  node_modules duplicate of react-native-windows is actually blocked.
• Add a resolveRequest hook redirecting react-native (and deep imports) to
  react-native-windows on the windows platform, ensuring a single renderer /
  view-config registry instance.

Verification

• Dev bundle now contains a single ReactNativeViewConfigRegistry
  (bundle size 10.1 MB → 5.09 MB).
• The example renders fully: all TurboModule outputs, both buttons, and the
  CircleMask native component (teal circle).

After fix - cpp-lib example rendering (CircleMask native component visible)

Microsoft Reviewers: Open in CodeFlow