Move SimpleFindWidget into base

[Tyriar]

Currently the new list view find box uses FindInput instead of SimpleFindWidget because the list lives in base, not workbench. We should give SimpleFindWidget the same treatment as HoverWidget to fix this. Ideally we would do this:

• Move SimpleFindWidget into base
• Allow injecting services into SimpleFindWidget for convenience when used in workbench (extending in platform?)
• Have the editor FindWidget extend SimpleFindWidget to reduce code duplication

cc @rebornix @joaomoreno @andreamah

[rebornix]

👍 for moving the SimpleFindWidget to a lower layer, along with some polish for the input box #156179

Note that moving the find widget to base/platform would mean that it would be more challenging to bring in rich features to the input box. For example, we were considering supporting syntax highlighting for regex mode to improve the readability of the regular expressions. This can be done by replacing the input/texarea with a simple monaco editor. Another one is keybinding support for the input/texarea, users are expecting to use the same keybindings from the text editor, which can easily be supported by replacing the input/texarea with monaco. If this is what we want to have in the future, we may want to consdier how to make the input box swappable.

[Tyriar]

Passing this to just @andreamah as I doubt I'll end up doing this and it's closely related to #155761