[makspll]

cargo run --example reactive_ui --features lua54: an inventory of 500 items which live in the ECS as Item components, shown and edited by a reactive ui in Lua (assets/scripts/inventory_ui.lua).

• ECS → ui: a Rust system restocks a few items five times a second. The ui watches the components, only the rows of the items which changed update, with no script code run (the rows are a row template)
• ui → ECS: clicking a slot selects it, the buttons of the selected item write to its Item component from the script. Rust systems see those like any change
• the bar at the top shows how long the last ui update took, measured by two systems around ReactiveUiSystems, and how often Rust restocked
• filters by kind, a details component with closures next to the templated list, context free: the two styles side by side
• editing the script while it runs reloads the ui and keeps its state

Also in this PR, needed by the example: ui.list, ui.list_template and ui.show take the properties of the node holding their children as a last argument, so a list can be laid out (a wrapping row here).

The root crate's dev dependencies gain the bevy features the example needs to draw and click a ui (bevy_ui_render, bevy_text, bevy_picking, ui_picking) and the ui crate.

Checked here by running a headless copy of the example for 200 frames: 500 rows mounted, counts following the restocking, no script errors. It could not be run in a window in this environment, so clicking through it is not verified.

Stacked on #730.

[semanticdiff-com]

Review changes with  

Changed Files

File	Status
crates/bevy_mod_scripting_reactive_ui/src/runtime.rs	62% smaller
crates/bevy_mod_scripting_reactive_ui/src/lib.rs	34% smaller
Cargo.toml	Unsupported file format
assets/scripts/inventory_ui.lua	0% smaller
docs/src/ReactiveUi/introduction.md	Unsupported file format
docs/src/ReactiveUi/reference.md	Unsupported file format
examples/reactive_ui.rs	0% smaller

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Bencher Report

Project	Bevy Scripting
Branch	agent/reactive-ui-example
Testbed	linux-gha

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