#1697 Update global context search sample to use country restrictions

[Anonymous]

Originally created by: KirtiRamchandani

Fixes [#1653].

Problem
The global context search sample still described and implemented country-specific Google searches by switching Google domains. That no longer produces a useful visible difference for users, which makes the sample feel outdated even though it still demonstrates the contextMenus API.

Root cause
The sample stored top-level-domain IDs and built URLs such as https://google.ca/search. Modern Google Search localizes results independently of those domains.

Solution

• Replace TLD options with country region codes.
• Build searches against https://www.google.com/search with the cr=countryXX parameter.
• Rename popup/storage variables to enabledRegions and update the README/manifest wording to match the new behavior.

Tests run

• npx eslint api-samples/contextMenus/global_context_search/background.js api-samples/contextMenus/global_context_search/popup.js api-samples/contextMenus/global_context_search/locales.js
• npx prettier --check api-samples/contextMenus/global_context_search/README.md api-samples/contextMenus/global_context_search/background.js api-samples/contextMenus/global_context_search/locales.js api-samples/contextMenus/global_context_search/manifest.json api-samples/contextMenus/global_context_search/popup.js
• URL-construction smoke test over all region options
• git diff --check origin/main..HEAD