extensions: await native metered state for automatic updates

[Dmitriy Vasyura (dmitrivMS)]

Stack

Stacked directly on #331897 (dev/dmitriv/use-vscode-metered). This PR contains only the extensions workbench portion of the original combined change and does not depend on the other consumer PRs. Merge the primary PR first, then retarget this PR to main.

Changes

• Route automatic update checks through native metered initialization for configuration, extension enablement, product update, allowed-extension, and connection changes.
• Wait for readiness in scheduled checks, built-in extension updates, and regular automatic extension updates.
• Preserve manual update checks and avoid starting or rescheduling work after disposal.
• Add initialization regression coverage and update the affected extension test doubles.

VS Code product-update service changes remain in the primary PR; this PR is specifically for extension updates.

Validation

• 366 tests passed across extension workbench, recommendations, actions, and views.
• Client type-check, targeted transpilation, and staged-file hygiene/ESLint passed.
• The diff is limited to five extension files. Applying all four disjoint sibling diffs to the primary branch exactly reconstructs the original combined PR tree.