feat: show final request variables under request vars tab

[jayakrishnancn]

Description

In the Request → Variables tab, display a table with:

resolves #5456

Variable Name – effective name used in the request
Value – resolved final value after applying precedence
Source – origin of the variable (Collection, Folder, Request, or Environment)
Notes:
2. Precedence: Request > Folder > Collection > Environment
3. View updates automatically when request or environment context changes

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• The pull request only addresses one issue or adds one feature.
• The pull request does not introduce any breaking changes
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[helloanoop]

See #5456 (comment)