Define cylinder and equirect initialization validation

[cabanier]

Fixes #333.

This change:

• Rejects invalid cylinder initialization values with TypeError for both WebGL and media layers.
• Explicitly clamps equirect initialization values consistently with existing attribute behavior.
• Refactors the shared initialization algorithms to accept resolved values from either WebGL or media dictionaries.
• Resolves media cylinder aspectRatio locally without mutating the input dictionary.
• Removes the unsupported infinity wording for an IDL float radius.

This update will bring the algorithms in the spec in line with the implemented behavior and normative language earlier in the spec.

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