ui: Autofocus search input on settings pages

[camillobruni]

When selecting a search page (flags, plugins or settings) autofocus directly on the search input to required fewer mouse inputs.

[github-actions]

🎨 Perfetto UI Build

✅ UI build is ready: https://storage.googleapis.com/perfetto-ci-artifacts/gh-21373958017-1-ui/ui/index.html

[stevegolton]

Unfortunately as pages are retained in memory even after switching away (in order to avoid losing things like scroll position), this only works the first time the pages are navigated to, which feels a little janky.

I'm not aware of an elegant solution to this problem, but open to suggestions.

[camillobruni]

Likely not the right place to add this – but this was the easiest for now.

[camillobruni]

Took another stab at this by adding a FocusPage that internally tracks the open state and update PageManagerImpl to pass along the open state to the render method too.

[stevegolton]

I'm not particularly keen on this approach because:

• Manual drilling of the 'open' state through potentially many layers of components.
• FocusPage needs oncreate and onupdate but it's all to easy to override by mistake in subclases.
• Only works with pages (not subpages, or tabs, which also mostly use Gate to control visibility).

I've been playing around with my take on this problem here: #4603 - I'd be interested to hear your thoughts.