Introduce the "builtin-style-elements.ts" that export all builtin styles to simplify the root "index.ts" file.
This simplifies the maintenance and will reduce the impact of the future refactoring on `EdgeStyle` and `Perimeter`.

Simplify default builtins registration using a loop as this is already done to register Shapes.

tbouffard deleted the refactor/reorg_builtin_style_elements branch

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