documentation: Adds migration advice, removes no-op deprecations

[dkbast]

documentation: Add link to migration guide and remove no-op deprecations and add deprecation messages with suggestions on how to change the code.

Adds the tipps from #852 to the migration document and adds #828 to the deprecation notice so you don't have to look around for the fix.

Tagging @dnfield for review

[dkbast]

Hi @dnfield - thanks for the quick review! I just did a migration on a bigger project and having many no-ops around made it a lot more difficult to migrate. It was hard to tell if I can still use a deprecated field or if it just doesn't do anything anymore - If they would still have any effect I would 100% agree, but '@deprecated' implies that this is still working but will not in the future.

From the docs: "The intent of the @Deprecated annotation is to inform authors who are currently using the feature, that they will soon need to stop using that feature in their code, even if the feature is currently still working correctly."

Please let me know if you still want me to reintroduce the dead code :) - no offence meant, the migration just did not go as smooth as you probably hoped to achieve

[felipecastrosales]

Very good, @dkbast. Congratulations on being proactive.