[makspll]

A "Reactive UI" section in the book's user guide:

• Introduction: the model in five lines, elements, reading and writing the ECS, shared state and context, reloading
• Coming From Another Framework: what carries over and what surprises, for React, signal frameworks (Solid, Preact Signals, Vue, Svelte), immediate mode (egui, Dear ImGui) and Bevy UI in Rust, each with a mapping table
• Performance: updating versus building, the three ways to write a property and the three ways to build a list with their measured costs, captures versus dependencies, rules of thumb
• Reference: elements, properties and their values, events, state, values computed in Rust, row templates, dependencies, mounting and testing, Rune differences

The numbers on the performance page are the ones measured in #723, #724, #725 and #726.

Stacked on #729.

[semanticdiff-com]

Review changes with