Fixes #304121

Problem

The Images Preview editor shows the default text-file icon in its modal header label, which doesn't represent image content:

Fix

ImageCarouselEditorInput never overrode getIcon(), so the label fell back to the default file icon. This change registers a dedicated icon and returns it from the input, following the same pattern used by other editor inputs (searchEditorInput.ts, chatDebugEditorInput.ts, extensionsInput.ts, etc.):

const imageCarouselEditorIcon = registerIcon('image-carousel-editor-label-icon', Codicon.fileMedia, localize('imageCarouselEditorLabelIcon', 'Icon of the images preview editor label.'));

// in ImageCarouselEditorInput
override getIcon(): ThemeIcon {
	return imageCarouselEditorIcon;
}

Notes:

• $(file-media) is proposed as the icon — happy to switch to a different codicon if preferred.
• Registering through registerIcon keeps the icon overridable by product icon themes, consistent with the other editor label icons.
• No rendering changes needed: the modal header (modalEditorPart.ts) already renders getIcon() via the resource label, and the icon is sized by the shared .monaco-icon-label styles like every other editor icon.

Before / After

Before:

After: