Refactor split helper documentation for clarity

[cathysarisky]

Updated the usage syntax for the split helper from {{split}} to {{#split}} and added additional examples for clarity, clarifying the behavior for empty strings.

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Note

Updates split helper docs to use {{#split}}, adds inline usage example, and documents filtering of empty strings.

• Docs: themes/helpers/utility/split.mdx
  • Update usage and references from {{split}} to {{#split}}.
  • Add Inline mode example using {{#foreach (split ...)}}.
  • Document behavior: filters out empty strings when separators are sequential, with example output.
  • Expand examples for custom separators and iteration with {{#foreach}}.

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