Bring back parallel tool calls

[mrubens]

Important

Re-enables experimental feature for multiple native tool calls, controlled by an experimental setting, and updates UI to reflect this change.

• Behavior:
  • Re-enables experimental feature for multiple native tool calls in presentAssistantMessage.ts and Task.ts.
  • Controlled by experiments.isEnabled with EXPERIMENT_IDS.MULTIPLE_NATIVE_TOOL_CALLS.
• UI:
  • Removes filter hiding MULTIPLE_NATIVE_TOOL_CALLS in ExperimentalSettings.tsx, making it visible in the UI.
• Misc:
  • Comments updated to reflect the change from a disabled feature to an experimental setting.

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[roomote]

Rooviewer   See task on Roo Cloud

Review complete. No issues found.

This PR correctly re-enables the parallel tool calls experimental feature by:

• Replacing hardcoded false values with proper experiment flag resolution in presentAssistantMessage.ts and Task.ts
• Removing the filter that was hiding MULTIPLE_NATIVE_TOOL_CALLS from the experimental settings UI

The implementation follows existing patterns, properly handles null/undefined state, and is consistent with existing tests.

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