[Excel] (Custom functions) Clean up repeating parameters guidance

[alison-mk]

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Pull Request Overview

This PR refreshes the Excel custom functions documentation by updating metadata, clarifying repeating-parameter rules, and consolidating declaration guidance.

• Bumped the document date to 06/26/2025.
• Added a note about repeating parameters needing to be last and unique.
• Reformatted examples (bold syntax) and merged TypeScript, JavaScript, and JSON instructions into a single declaration section.

Comments suppressed due to low confidence (3)

docs/excel/custom-functions-parameter-options.md:220

• [nitpick] Use '### Declaring repeating parameters' to maintain consistency with the noun-based style of other section headings.

### Declare repeating parameters

docs/excel/custom-functions-parameter-options.md:222

• Add a comma after 'For example' ('For example, in TypeScript, …') to improve readability and adhere to standard grammar.

To declare a repeating parameter, indicate that the parameter is multi-dimensional. For example in TypeScript, `ADD(values: number[])` would indicate a one-dimensional array, `ADD(values:number[][])` would indicate a two-dimensional array, and so on. In JavaScript, use `@param values {number[]}` for one-dimensional arrays, `@param <name> {number[][]}` for two-dimensional arrays, and so on for more dimensions.

docs/excel/custom-functions-parameter-options.md:224

• Wrap the JSON keys repeating and dimensionality in backticks to clearly distinguish them as code elements.

For [manually-created JSON metadata](custom-functions-json.md), ensure that the parameter is specified as `"repeating": true` and `"dimensionality": "matrix"` in your JSON file.