Backfilling Web Widgets

### What is the problem or limitation you are having?

The Toga web platform currently lacks implementations for a number of standard widgets that are available on other platforms. Which is currently limiting the ability to build-cross platform applications.

### Describe the solution you'd like

We plan to implement the missing widgets in the web back end to bring it closer to feature parity with other supported platforms.

Proposed Widgets

- [x] DateInput - Completed [#3338](https://github.com/beeware/toga/pull/3338) @mEp3ii2
- [x] TimeInput - Completed [#3405](https://github.com/beeware/toga/pull/3405) @JMah007
- [ ] NumberInput - In Progress [#3299](https://github.com/beeware/toga/pull/3299) @LunaMeadows
- [x] Selection - Completed [#3402](https://github.com/beeware/toga/pull/3402)@vt37
- [x] Slider - Completed [#3527](https://github.com/beeware/toga/pull/3527)@vt37
- [ ] Tree
- [ ] WebView
- [ ] MultilineTextInput
- [ ] DetailedList
- [ ] ImageView In Progress @Stringer90
- [ ] MapView
- [ ] Option Container
- [x] ScrollContainer Completed [#3362](https://github.com/beeware/toga/pull/3362) @kavi2du
- [ ] SplitContainer
- [ ] Table

### Describe alternatives you've considered

Do nothing

### Additional context

[https://github.com/beeware/toga/discussions/3333](url)

No files, tests, or entry points are named. Start by choosing one unchecked widget and compare the web back end with the corresponding implementations on other platforms. Done means that widget is implemented in the web back end and the checklist can be updated.

Written by the indexing model from the issue text.