Port TypeScript PR #60195: Assume that type node annotations resolving to error types can be reused

[Copilot]

This PR ports the changes from TypeScript PR #60195 to prevent cascading errors in isolated declarations when type annotations resolve to error types.

Problem

When a type annotation resolves to an error type (e.g., due to an unresolved import), the type checker would previously refuse to reuse the existing type node, leading to additional confusing error messages beyond the original resolution error.

Solution

Added an early return in tryReuseExistingNonParameterTypeNode that allows type node reuse when the annotation type is an error type. This prevents cascading errors while maintaining correct behavior for valid types.

Key changes:

• Added check if annotationType != nil && b.ch.isErrorType(annotationType) after resolving annotation type
• Return existing type node to allow reuse when annotation resolves to error type
• Includes the same explanatory comment from the original TypeScript change

Example

// This would previously generate cascading errors
import { Unresolved } from "nonexistent-module"; // Error: Cannot find module

export const foo = (param?: Unresolved): void => {}; // No additional confusing errors

The change ensures that when Unresolved fails to resolve, we don't generate additional type mismatch errors for the parameter type annotation.

Testing

• All existing tests pass
• No baseline changes required (change only affects error cases)
• Verified the fix resolves the null pointer dereference that occurred during testing

Fixes #1118.

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