Use virtual scrolling for Emoji picker

[efstajas]

Currently, performance is super poor when opening a step that includes an Emoji picker (e.g. edit project), because hundreds of DOM elements are being injected.

Our List Editor component already uses a virtual scrolling library in order to handle displaying potentially thousands of items without sacrificing performance.

We should use some kind of virtual scrolling solution, ideally the same one, for the Emoji picker too, so that only the rows in view (or almost in view) are rendered.