Fix Text object position after string updates

[2bf]

Fixes #975.

This keeps the Pixi text renderer position in sync after a Text object's string changes. PIXI.Text.updateText(false) recalculates the rendered text metrics, so the renderer also needs to call updatePosition() afterward; otherwise a rotated Text object can keep the old center/anchor placement and appear to move as the displayed string changes width.

This matches the existing BBText and BitmapText renderer behavior, where text-content updates already refresh positioning.

Validation:

• git diff --check

I made the change in a sparse checkout, so I did not run the full GDevelop test suite locally.

[2bf]

CI note: the failed checks look unrelated to this renderer change.

Semaphore fails in newIDE typing and newIDE tests while parsing the downloaded libGD.js artifact:

• newIDE typing: ../public/libGD.js reports TS1128: Declaration or statement expected
• newIDE tests: Jest fails to parse node_modules/libGD.js-for-tests-only/index.js with the same generated artifact content

Travis fails earlier in the native C++ loop: Core/GDCore_tests segfaults repeatedly and exits with 139. The later JS checks in the same Travis job pass (npm test, Flow, formatting, and script type checks).

This PR only changes Extensions/TextObject/textruntimeobject-pixi-renderer.ts, so these appear to be CI/artifact or native-test failures rather than failures from the position update fix.