fixes #81630

This helps with lifecycle tracking

Readonly helps with type guards and code comprehension

Const is preferred for type guards

We compile using the alwaysStrict flag so these directives are not needed

This part removes most `use strict` directives that are right after the file header

* have explicit methods for changing the scroll position (delayed/smooth vs now/direct) that bubble up to the editor internals.
* have all other clients of ScrollableElement not use smooth scrolling

Fixes Microsoft/monaco-editor#2: Fix scrollbars, context menus, mouse operations and content widgets layouting when editor is inside a position:fixed container