Remove deprecated FeedbackWidget API aliases

## Description

In #5931 we renamed `FeedbackWidget` to `FeedbackForm` and added deprecated aliases for backward compatibility. These should be removed in the next major version.

### Deprecated aliases to remove

- `FeedbackWidget` → `FeedbackForm` (`index.ts`)
- `showFeedbackWidget` → `showFeedbackForm` (`index.ts`, `FeedbackFormManager.tsx`)
- `FeedbackWidgetProps` → `FeedbackFormProps` (`FeedbackForm.types.ts`)
- `FeedbackWidgetStyles` → `FeedbackFormStyles` (`FeedbackForm.types.ts`)
- `FeedbackWidgetState` → `FeedbackFormState` (`FeedbackForm.types.ts`)
- `FeedbackWidgetTheme` → `FeedbackFormTheme` (`FeedbackForm.theme.ts`)
- `FeedbackWidgetManager` → `FeedbackFormManager` (`FeedbackFormManager.tsx`)
- `resetFeedbackWidgetManager` → `resetFeedbackFormManager` (`FeedbackFormManager.tsx`)

### When

Next major version (v9).