Improve log in handling for Google

[robertsreberski]

Proposed Changes

• Change authentication flow to use redirectToLogout instead of logoutUser for Jetpack social logins (Google, Apple, GitHub)
• Fix error handling in Google auth callback to silently continue when user already exists
• Simplify Apple authentication by using a local random nonce generation instead of API request
• Ensure consistent logout handling across all social authentication methods
• Improve code structure with early returns for logged-in users in authentication flows

[github-actions]

Calypso Live (direct link)

https://calypso.live?image=registry.a8c.com/calypso/app:build-138820

Jetpack Cloud live (direct link)

https://calypso.live?image=registry.a8c.com/calypso/app:build-138820&env=jetpack

Automattic for Agencies live (direct link)

https://calypso.live?image=registry.a8c.com/calypso/app:build-138820&env=a8c-for-agencies

[matticbot]

Here is how your PR affects size of JS and CSS bundles shipped to the user's browser:

App Entrypoints (~14 bytes added 📈 [gzipped])

Details

name         parsed_size           gzip_size
entry-login       -133 B  (-0.0%)      +14 B  (+0.0%)

Common code that is always downloaded and parsed every time the app is loaded, no matter which route is used.

Legend

What is parsed and gzip size?

Parsed Size: Uncompressed size of the JS and CSS files. This much code needs to be parsed and stored in memory.
Gzip Size: Compressed size of the JS and CSS files. This much data needs to be downloaded over network.

Generated by performance advisor bot at iscalypsofastyet.com.

[Copilot]

Pull Request Overview

This PR improves the social authentication flows by updating the logout handling, refining error handling in Google auth callback, and simplifying the authentication nonce generation for Apple logins.

• Replace logoutUser with redirectToLogout for consistent logout behavior.
• Modify error handling in Google auth callback to silently ignore user existence errors.
• Simplify Apple authentication by using a locally generated nonce.

[Copilot]

The catch block in jetpackGoogleAuthCallback silently swallows all errors, which may mask unexpected issues. Consider filtering errors to only ignore the specific 'user already exists' case or log other errors for debugging purposes.

Suggested change

	// Silently fail: user already exists
	if (createError.message.includes('user already exists')) {
	// Silently fail: user already exists
	} else {
	console.error('Unexpected error during user creation:', createError);
	}