fix: use instanceof instead of constructor name in formatErrors

[mahmoodhamdi]

What

Fixes formatErrors silently dropping the data field from APIError responses in production builds.

Closes #16050

Why

formatErrors used proto.constructor.name string comparison to identify APIError and ValidationError instances. In production, webpack/terser minifies class names (e.g., APIError → t), causing the check to fail. This silently drops error.data, breaking any feature that relies on it — for example, 2FA flows that check data.requires2FA.

The APIErrorName/ValidationErrorName module variables were designed to handle this via dynamic reassignment in constructors, but minifiers can inline the initial string value at import sites, defeating the mechanism.

Changes

• Replaced proto.constructor.name === APIErrorName / ValidationErrorName checks with instanceof APIError / instanceof ValidationError
• For the Mongoose ValidationError fallback (which isn't a Payload class), switched to checking incoming.name === 'ValidationError' — a string property that Mongoose sets explicitly and isn't affected by minification
• Removed unused APIErrorName / ValidationErrorName imports

Why instanceof is safe here

The original code avoided instanceof citing TypeScript#13965, where instanceof fails for classes extending Error when transpiled to ES5. However:

• Payload's tsconfig targets ES2022, so native class syntax is preserved
• instanceof works correctly with ES2015+ classes extending Error
• The original workaround itself was broken by minification — a worse failure mode

Testing

• npx tsc --noEmit passes with no errors
• Verified that Payload's ValidationError (which has data) is caught by the instanceof branch and never falls through to the Mongoose branch
• The Mongoose ValidationError check uses the name property which Mongoose sets explicitly (this.name = 'ValidationError') — not affected by minification