fix: Create an ElementInput in Application

[willeastcott]

<Application> creates the mouse and touch devices but no ElementInput, the object that turns input into events on element components. Without it, <Element useInput> receives no events, buttons added to elements never react, and scroll views and scrollbars can't be dragged. The engine only reports it through a debug-build warning, so in a production build the UI is silently inert.

This creates one when the application is created. It is created before the mouse and touch devices, so its window listeners run first: calling stopPropagation() in a UI event handler then also keeps the event from app.mouse and app.touch (for example, app.mouse.wasPressed() stays false for a click on a button), which is the order the Editor's launcher uses.

Checked in Chrome with engine 2.22.4: with no other setup, a button's click, an element's click and mousedown fire, and stopPropagation() on mousedown keeps app.mouse.wasPressed() false, in StrictMode too. <Entity onClick> picking still works alongside it.

The test setup's mock Application now passes the elementInput option through, so a new test can check that the application has one and that it is bound to the app. A changeset is included (patch).

Found while rewriting the User Interface chapter of the User Manual; its React examples would otherwise need a wrapper component that creates the ElementInput and re-attaches the mouse and touch devices.

🤖 Generated with Claude Code

[changeset-bot]

🦋 Changeset detected

Latest commit: 503f52e

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 2 packages

Name	Type
@playcanvas/react	Patch
@playcanvas/blocks	Patch

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commit: 503f52e