Use WebP as default image format instead of PNG + suggestion

[arno974]

By default, the image format for a layer is PNG. I suggest switching the default image format from PNG to WebP to benefit from smaller file sizes, better compression, transparency support, and modern web compatibility."

Additionally, it would be helpful to have an option to modify layer settings (for example image format) all at once instead of one by one. In projects with dozens of layers, this feature would save a significant amount of time.