Fix TilemapGPULayer rendering at double its position

[moufmouf]

This PR (delete as applicable)

• Fixes a bug

A TilemapGPULayer placed at (x, y) was rendered at (2x, 2y). The layer's position is already baked into the transform via applyITRS(x, y, ...), but setQuad() was then called with the absolute x/y again, applying the offset twice.

The existing GPU tilemap examples only place layers at (0, 0), so the doubling (2*0 = 0) was never visible and the bug went unnoticed.

A full repro is available in this fork of the examples repository: moufmouf/examples@4e831f6

class Example extends Phaser.Scene
{
    preload ()
    {
        this.load.image('tiles', 'assets/tilemaps/MedievalRTS/medieval_tilesheet.png');
        this.load.tilemapTiledJSON('map', 'assets/tilemaps/MedievalRTS/sample.json');
    }

    create ()
    {
        const OX = 250;
        const OY = 180;

        const map = this.make.tilemap({ key: 'map' });
        const tileset = map.addTilesetImage('medieval_tilesheet', 'tiles', 64, 64);

        // GPU tilemap layer (5th argument = true), positioned at (OX, OY).
        map.createLayer('Land', tileset, OX, OY, true);

        // Marker for the expected top-left corner of the layer.
        this.add.rectangle(OX, OY, 64, 64).setStrokeStyle(2, 0xff00ff).setOrigin(0, 0);
        this.add.text(OX, OY - 22, `createLayer('Land', ts, ${OX}, ${OY}, true)`, {
            fontFamily: 'monospace', fontSize: 15, color: '#ff00ff'
        });
    }
}

Result before the fix:

Result after the fix: