Stable release of 2021 group

[laugengebaeck]

What does this change?

[Feature] Adds all changes from the 2021 group to the master branch.

Checklist

• [x] Your branch has no merge conflicts with master
• [x] All related commits are squashed together

[coveralls]

Pull Request Test Coverage Report for Build 1105324170

• 487 of 534 (91.2%) changed or added relevant lines in 120 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+19.5%) to 91.953%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
packages/IMAPClient-Core.package/ICConnectionHandler.class/instance/checkLoggedIn.st	0	1	0.0%
packages/IMAPClient-Core.package/ICConnectionHandler.class/instance/refreshConnectionProcess.st	0	1	0.0%
packages/IMAPClient-Core.package/ICEndPoint.class/instance/retrieveBody..st	0	2	0.0%
packages/IMAPClient-Core.package/ICFolder.class/instance/fetchNumberOfLatestEmails..st	0	2	0.0%
packages/IMAPClient-Core.package/ICConnectionHandler.class/instance/preventTimeout.st	0	4	0.0%
packages/IMAPClient-Core.package/ICEndPoint.class/instance/readEmailsFromDisk.st	0	4	0.0%
packages/IMAPClient-Core.package/ICEndPoint.class/instance/currentUIDsFor..st	0	6	0.0%
packages/IMAPClient-Core.package/ICEndPoint.class/instance/maildirDiffFetchHeadersFor.from..st	0	9	0.0%
packages/IMAPClient-Core.package/ICFolder.class/instance/startUIDFor..st	0	9	0.0%
packages/IMAPClient-Core.package/ICFolder.class/instance/updateAndShowProgressWith..st	0	9	0.0%
<!--	Total:	487	534	91.2%	-->

Totals
Change from base Build 199376006:	19.5%
Covered Lines:	1394
Relevant Lines:	1516

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💛 - Coveralls