Fix a memory leak when calling setMultiDraw

[AlexAPPi]

I noticed a memory leak when calling setMultiDraw several times in a row.
Allocate is always called, which results in the creation of a StorageBuffer while the previous buffer is not deleted.

engine/src/scene/mesh-instance.js

Line 1224 in d09fd9f

cmd.allocate(maxCount);

engine/src/platform/graphics/webgpu/webgpu-draw-commands.js

Line 42 in d09fd9f

this.storage = new StorageBuffer(this.device, this.gpuIndirect.byteLength, BUFFERUSAGE_INDIRECT | BUFFERUSAGE_COPY_DST);

It would also be good if old data was saved and not reset then allocate.

    /**
     * Allocate AoS buffer and backing storage buffer.
     * @param {number} maxCount - Number of sub-draws.
     */
    allocate(maxCount) {
        this.storage?.destroy(); // <--- DISPOSE EXISTS
        this.gpuIndirect = new Uint32Array(5 * maxCount);
        this.gpuIndirectSigned = new Int32Array(this.gpuIndirect.buffer);
        this.storage = new StorageBuffer(this.device, this.gpuIndirect.byteLength, BUFFERUSAGE_INDIRECT | BUFFERUSAGE_COPY_DST);
    }