fix(core): slash ask ai returns make it real action result (#10349)

Fix issue [AF-2252](https://linear.app/affine-design/issue/AF-2252).

## What Changed?
- Remove useless `generateAnswer` configuration for inline ask ai
- Refactor the common `updateAIPanelConfig` function
- Use empty string instead of meaningless `placeholder` string
- Remove unnecessary high-order function wrappers

blocksuite/affine/block-root/src/widgets/ai-panel/ai-panel.ts

@@ -278,7 +278,7 @@ export class AffineAIPanelWidget extends WidgetComponent {
     input?: string,
     shouldTriggerCallback?: boolean
   ) => {
-    if (input) {
+    if (typeof input === 'string') {
       this._inputText = input;
       this.generate();
     } else {