[cherry-pick] NES: enable trigger on active editor change by default

[vs-code-engineering]

Cherry-pick of #309489 from main.

Summary

Enable NES triggering on active editor change by default and improve same-line cooldown behavior.

Changes

Default config changes:

• triggerOnEditorChangeAfterSeconds: undefined → 10 — NES now triggers when switching editors by default
• triggerOnEditorChangeStrategy: Always → AfterAcceptance — document switch only triggers NES if the last suggestion was accepted

Same-line cooldown behavior change:

• Before: When triggerOnEditorChangeAfterSeconds was set, the same-line cooldown was completely disabled — every cursor move on the same line re-triggered NES
• After: Same-line cooldown is always enforced within a file session but resets when switching away and returning. Example:
  1. User triggers NES in file A on line 10 → cooldown active
  2. Cursor moves on same line → blocked by cooldown
  3. User switches to file B → file A's line cooldowns are cleared
  4. User returns to file A, line 10 → triggers again

Test updates

• Added lastOutcome = NesOutcome.Accepted to document-switch tests (needed with AfterAcceptance default)
• Rewrote cooldown bypass test to verify the new switch-away-and-back behavior