Change research behaviour

Hi,
Here is the wanted behaviour of the research :

- When user clicks on "search" icon button (magnifying glass), the files list is cleared and a "search" instruction (like on iOS app) is shown, with something like "Type something to search (2 characters min.)"
- When user types something, 300ms after end of typing (debounce), the term is searched (or early if user press enter on keyboard)
- If user clicks on "X" (cross) on right of field, we return to the original RESEARCH state ("Type something to search [...]")
- If user clicks on arrow/back, it cancels the research and return to the original FILES LIST state.

It has been discussed here : https://github.com/nextcloud/android/issues/5000
The "bug part" has been fixed, but the wanted behaviour has to be developed.

So I create this issue to keep the "enhancement" part.