adding prompt completions

[aiday-mar]

No description provided.

[Copilot]

Pull request overview

This PR updates the chat input editor to support “prompt completions” by enabling the inline completions contribution on the chat input CodeEditorWidget, and adjusting editor/model options to fit that experience.

Changes:

• Adds InlineCompletionsController to the chat input editor’s contributions list.
• Disables quickSuggestions for the chat input editor.
• Changes the chat input model creation to use isForSimpleWidget = false.

[Copilot]

Changing createModel(..., /*isForSimpleWidget*/ false) makes the chat input text model eligible for synchronization to the extension host (shouldSynchronizeModel filters out only model.isForSimpleWidget). This is a significant behavior change: extensions will start receiving open/change events for chatSessionInput: documents, which can both expose user-entered prompts and add per-keystroke IPC/extension overhead. If the goal is to enable inline/prompt completions, consider keeping this model as a simple widget and proxy only the data needed for completions, or otherwise add an explicit rationale/guardrails for syncing this scheme to extensions.

Suggested change

	inputModel = this.modelService.createModel('', null, this.inputUri, false);
	// Mark as simple widget to avoid synchronizing chat input to the extension host
	inputModel = this.modelService.createModel('', null, this.inputUri, true);