OT: Research SplitOperation#insertionPosition transformation

[scofalik]

📝 Provide a description of the improvement

Followup for #8870.

In #8870 I found a bug that happened in some undo scenarios involving split operation. Upon research, it appeared that in split x insert transformation, SplitOperation#insertionPosition is transformed in a, let's say, naive way, that in some scenarios was incorrect. This only concerns split operations that are a result of undo (so, reversed merge operations).

SplitOperation#insertionPosition is transformed in multiple places in OT and it could be incorrectly transformed in some of them as well.

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