Initial 1.20.6 support (#2616)
* 1.20.5 part 1: bump version numbers
* 1.20.5 part 2: bulk update revision number
* 1.20.5 part 3: initial changes to make it compile
* Few minor fixes
* Bump paper version
* Account for `ItemFlag` naming change
* Compile against 1.20.4 for old version support
* Bump to 1.20.6
* Bump `TODO`s as well
* Compact with older versions
* Remove profile handling TODO
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commit: 4f24205)
