fix(input): pierce shadow DOM in onTouchMove over-canvas detection

[pauliojanpera]

This PR

• Fixes a bug

Describe the changes below:

InputManager.onTouchMove used document.elementFromPoint() to decide whether a touch is over the canvas. When Phaser runs inside a shadow root, that call resolves to the shadow host rather than the canvas, so overCanvas is always false, isOver latches false, and every touchmove inside the shadow root is silently dropped — pointer.x/y never update on touch devices.

Use the canvas's root node (canvas.getRootNode(), a ShadowRoot when inside shadow DOM, otherwise the Document) which exposes elementFromPoint and resolves the topmost element across the shadow boundary. Falls back to document when the root node has no elementFromPoint.

Reproduction

A self-contained, single-file repro that demonstrates the bug:

• Source (gist): https://gist.github.com/pauliojanpera/1a8dab1e2cfaffb103812d0ce7481056
• Live (githack): https://gist.githack.com/pauliojanpera/1a8dab1e2cfaffb103812d0ce7481056/raw/phasershadowdomtouchmoverepro.html

It mounts a Phaser game whose canvas is created inside an open shadow root and logs two independent event streams: a raw DOM touchmove listener on the canvas, and Phaser's own pointermove. Open the live link and drag inside the dark area on a touch device (or with DevTools touch emulation: Ctrl/Cmd+Shift+M).

• Before this fix (pinned phaser@3.90.0): the raw touchmove events fire, but Phaser pointermove never fires for touch, and the status bar turns red — "BUG REPRODUCED". A mouse drag still logs pointermove, since the mouse path never calls elementFromPoint — so only the touch path is broken.
• After this fix (swap the <script src> for a build containing the patched InputManager.js): touchmove and pointermove fire together and the status bar turns green.