Add move/copy-to-account

[mbalduccini]

Fixes issue #760.
The approach is fairly straightforward:

• I extended the relevant methods to take the destination account
• If the destination account is different from the source account, the message is copied over using MessageStore.saveLocalMessage()
• In case of a move, the source message is deleted
• Move/copy of threads is supported

It doesn't break any tests as far as I can tell. There are 11 tests that fail on my computer, and they are the same tests that fail in the main branch. Screenshots attached.

[cketti]

The failing protocol tests might be because the tests were run using an (old?) JDK without an "unlimited cryptography policy". See https://www.java.com/en/configure_crypto.html

The failing tests in QuoteDateFormatterTest are also related to the Java version used to run the tests. #8651 should work around this, though.

In general it's probably best to use the same Java version our GitHub workflow is using. Currrently that's Java 17.

[mbalduccini]

I switched to Java 17 (I was using 21) and things got a little better. The *ServerSettingsValidatorTest tests no longer fail. The RealImapConnectionTest test still fails as well as the tests in QuoteDateFormatterTest. I am attaching the screenshots.
@cketti I see that there are conflicts on three files. Would you like me to resolve them?

[mbalduccini]

@cketti I merged your latest changes including #8651. All tests pass now.

[cketti]

Thanks for working on adding support for moving messages from one account to another ❤️

Unfortunately, the suggested change only works in the best case and doesn't support error handling and recovery at all. Mostly that's because the necessary infrastructure for that is not in place. I listed (some of) the things that need to be considered here: #760 (comment)

There's a lot of changes we need to make to MessagingController and how we handle pending commands before this feature can be implemented in a reliable way. I'm working on writing all of this down, so we can devise a plan to incrementally work towards getting there.

I don't think it would be reasonable to put all of the necessary changes in one pull request. So my recommendation is to close this pull request.