ImageUtils: Add optional type parameter to getDataURL().

[Mugen87]

Related issue: -

Description

The PR adds an optional type parameter to ImageUtils.getDataURL() so it's possible to request other image formats than image/png.

Also uses ImageUtils.getDataURL() in GLTFExporter now.

[github-actions]

📦 Bundle size

Full ESM build, minified and gzipped.

	Before	After	Diff
WebGL	336.02 78.26	336.02 78.26	+0 B +0 B
WebGPU	525.13 146.26	525.13 146.26	+0 B +0 B
WebGPU Nodes	524.59 146.16	524.59 146.16	+0 B +0 B

🌳 Bundle size after tree-shaking

Minimal build including a renderer, camera, empty scene, and dependencies.

	Before	After	Diff
WebGL	465.06 112.14	465.07 112.14	+4 B +4 B
WebGPU	597.9 162.52	597.91 162.53	+4 B +8 B
WebGPU Nodes	553.03 152	553.03 152.01	+4 B +7 B