Add missing return type diagnostics and quick fixes

[eramitgupta]

Summary

Adds a new return type feature for PHP methods/functions in the Laravel VS Code extension.

This change:

• shows a diagnostic when a function/method is missing a return type
• does not show a diagnostic when a return type is already declared
• adds quick fixes to insert a suggested return type
• includes test coverage for common PHP return types and model return types

What was added

• New returnType diagnostic provider
• Diagnostic registry wiring for returnType
• Config support for Laravel.returnType.diagnostics
• Quick fix suggestions for missing return types
• Test fixture and test suite for return type behavior

Covered return type cases

The feature now avoids warnings when a return type already exists, including examples like:

• array
• int
• string
• mixed
• ?string
• ?int
• string|array
• Countable&Traversable
• static
• model return types like User
• framework/class return types like RedirectResponse

Quick fix behavior

When no return type is declared, the extension now suggests adding one.
Examples of inferred suggestions:

• return []; -> : array
• return "text"; -> : string
• return 1; -> : int
• return true; -> : bool
• return new User(); -> : User
• return; or no return value -> : void

A fallback : mixed quick fix is also provided.

Tests

Verified with:

• npm run check-types
• npm test -- --grep "Return Type Test Suite"

Notes

This feature currently checks whether a return type is declared and offers suggestions when missing.
It does not yet validate whether the declared return type matches the actual returned value.