965432: Need to add section in Defined name section with public method details and their scope

[DeiraSF4418]

Description:

The addDefinedName method in the Spreadsheet component allows developers to create custom named ranges or constants that can be reused in formulas. However, the current documentation lacks clarity on the usage of the referTo and scope properties.

To improve understanding, we must document:

• How to use the addDefinedName method.
• How the referTo value can be passed with or without the = prefix.
• The purpose and behavior of the scope property, including its default behavior when omitted.
• Usage examples for both globally scoped and sheet-scoped defined names.
• This addition will help users apply named ranges more effectively and understand their accessibility across sheets.

Task link - https://dev.azure.com/EssentialStudio/Ej2-Web/_workitems/edit/965432
Content link - https://github.com/syncfusion-content/ej2-asp-core-mvc-docs

[SyncfusionBuild]

Build Status: INPROGRESS 🔃
Build Location: EJ2-965432-hotfix

[SyncfusionBuild]

CI Status: FAILURE ❌
Source Compilation: SUCCESS ✅
Failure Reason: CI Failure with violation
Build Location: EJ2-965432-hotfix
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