Add justified text support to text elements

[mvaligursky]

Fixes #4633.

Adds justified text to element components, fixing #4633. Wrapped lines are stretched to be flush with both edges of the element by widening the gaps between their words.

Changes:

• New justify property on text elements, off by default. It only has an effect when wrapLines is true and the element has a width of its own to wrap against.
• Lines that must not be stretched are excluded: the last line of the text, lines ended by an explicit line break, and lines with no gaps to widen (a single long word). Those keep following alignment, which is what decides where they sit — the same split as CSS text-align and text-align-last.
• Line breaking is unaffected. Lines are broken at their natural widths first and justification is applied afterwards as a positioning pass, so turning it on never reflows the text.
• Works with right-to-left text, where a justified line is flush with both edges in the same way.
• Plumbed through addComponent data and clone() alongside the other text properties.

API Changes:

• Added ElementComponent#justify (boolean, defaults to false).

entity.addComponent('element', {
    type: pc.ELEMENTTYPE_TEXT,
    text: paragraph,
    wrapLines: true,
    autoWidth: false,
    width: 620,
    justify: true,
    alignment: new pc.Vec2(0, 1)  // still positions the last line
});

Examples:

• New user-interface/text-justify example, with a toggle for justify and a selector for alignment so the two can be combined, and a readout of the resulting values.

Performance:

• No effect when justify is false: the per-glyph gap offset is only read for lines that are actually being stretched.

[github-actions]

Public API report

This PR changes the public API surface (+2 / −0), per the docs' rules (@ignore / @Private / undocumented are excluded).

Show API diff

+ElementComponent.get justify(): boolean
+ElementComponent.set justify(arg: boolean)

Informational only — this never fails the build.

[github-actions]

Build size report

This PR changes the size of the minified bundles.

Bundle	Minified	Gzip	Brotli
playcanvas.min.js	2367.2 KB (+0.7 KB, +0.03%)	608.0 KB (+0.3 KB, +0.06%)	472.2 KB (+0.4 KB, +0.08%)
playcanvas.min.mjs	2364.6 KB (+0.7 KB, +0.03%)	606.9 KB (+0.3 KB, +0.05%)	471.3 KB (+0.2 KB, +0.04%)

[Copilot]

Pull request overview

Adds justified wrapping support to text element components.

Changes:

• Adds the public justify property and layout logic.
• Supports initialization, cloning, RTL layout, and tests.
• Adds an interactive justification example.

Reviewed changes

Copilot reviewed 6 out of 8 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
src/framework/components/element/text-element.js	Implements justified glyph positioning.
src/framework/components/element/component.js	Exposes the public API.
src/framework/components/element/system.js	Supports initialization and cloning.
test/framework/components/element/text-element.test.mjs	Tests justification behavior.
examples/src/examples/user-interface/text-justify.example.mjs	Demonstrates the feature.
examples/src/examples/user-interface/text-justify.controls.jsx	Adds example controls.

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[Copilot]

Pull request overview

Copilot reviewed 6 out of 8 changed files in this pull request and generated no new comments.