docs: convert Stepper/Tabs/Timepicker example to signals

[msmallest]

Description

Converts the following components to use signals

Part of an effort to address this issue about compatibility with new defaults: #33443

• Stepper
• Tabs
• Timepicker

Same callout as a previous change (but for a tab example, tab-group-dynamic-example.html):

I also switched one loop from tracking by identity to an index. This was because the diffing algorithm was throwing template warnings about how the array had multiple non-unique instances because 'New' can be added over and over.

PR Scope

3 component examples updated

Extras

1. Reference checklist gist: https://gist.github.com/msmallest/f77adb004b9e88c49b3a248bab90a26a?permalink_comment_id=6237328#gistcomment-6237328
2. I have been kicking the can on auditing Tables. There is just so many, and I have to investigate some changes more deeply. I may just move onto CDK change chunks first while I test out some table updates on the side.