`ViewImpl` follow the open–closed principle

ViewImplis directly depend on viewParts implementation, like:

import { Margin } from 'vs/editor/browser/viewParts/margin/margin';
import { Minimap } from 'vs/editor/browser/viewParts/minimap/minimap';

And keep viewParts private, that make custom Margin, Minimap logic without modify source code impossible.
But for users of this library, it's a natural request that extend the original editor feature by compose/extend the original implementation without touch source code.

Start by reading src/vs/editor/browser/view/viewImpl.ts and the imported viewParts implementations, including Margin and Minimap. Trace how ViewImpl owns and constructs these parts, then review the surrounding editor view APIs. Done should be a decided extensibility design that allows custom view-part behavior without modifying the source implementation.