More idiomatic texture atlas builder

[s-puig]

Objective

• TextureAtlasBuilder has some non-idiomatic methods.

Solution

• Refactor non-idiomatic methods

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Changelog

• Renamed TextureAtlasBuilder.finish() to build()
• TextureAtlasBuilder.with_texture() now consumes self and returns Self

Migration Guide

- texture_atlas_builder.add_texture(Some(id), texture);
+ texture_atlas_builder = texture_atlas_builder.add_texture(Some(id), texture);

- let (texture_atlas_layout, texture) = texture_atlas_builder.finish().unwrap();
+ let (texture_atlas_layout, texture) = texture_atlas_builder.build().unwrap();