Oauth2: docs refer to deprecated classes

[lbruun]

The following classes are deprecated in Spring Security 6.4+.

• DefaultAuthorizationCodeTokenResponseClient
• DefaultRefreshTokenTokenResponseClient
• DefaultClientCredentialsTokenResponseClient
• DefaultJwtBearerTokenResponseClient
• DefaultTokenExchangeTokenResponseClient

The docs at Spring Security OAuth2 should be changed to refer to the new recommended replacements, except in the cases where the docs specifically refer to how you would accomplish something prior to v6.4 (there is quite a bit of "how you would do it prior to 6.2" in the docs)

Obviously, this change must not be backported beyond 6.4.