fix: install git extension fs-copyfile dependency

[cyphercodes]

Fixes #7806

Summary

• Hoist the VS Code git extension's @vscode/fs-copyfile runtime dependency into the shared lib/vscode/extensions install manifest used by code-server's npm postinstall.
• Generate the extensions shrinkwrap from a temporary patched manifest so the released npm package installs @vscode/fs-copyfile deterministically without mutating the VS Code submodule package files.
• Add script coverage for the dependency-hoisting helper.

Test plan

• ./ci/dev/lint-scripts.sh
• npm run test:scripts
• Temporary install/resolve smoke test: generated the extensions package lock with @vscode/fs-copyfile, installed production dependencies, and verified require.resolve("@vscode/fs-copyfile", { paths: ["<tmp>/git/dist"] }) resolves from extensions/node_modules.
• git diff --check HEAD~1..HEAD