further compactification of writeTo

enabled an automatic merge when the pipeline for 25aea4dc succeeds

aborted the automatic merge because source branch was updated

added 21 commits

• 25aea4dc...343822df - 11 commits from branch main
• 88f24b55 - + XML::readTaggedElement, use once
• ac7e9082 - use readTaggedElement with reference
• eb358b6c - use readTaggedElement with pointer
• 69bf69eb - .
• 954f6df1 - + ProjectDocument::readFrom
• b4265cc2 - use XML::readTaggedElement
• d9d554e5 - InstrumentItem vs ScanningInstrItem: serialize only direct base class
• 8a6407f9 - + XML::readBaseElement, use once
• 58a402ee - use it everywhere
• 227bfff0 - manual fix

Compare with previous version

enabled an automatic merge when the pipeline for 227bfff0 succeeds

merged

mentioned in commit 40253584