After SERVER-88523, WiredTigerRecordStore::_insertRecords() handles:

• Inserting records (oplog entries) into the oplog
  • Additionally, it seems to be possible to insert oplog entries WITHOUT recordIds provided
• Inserting records into collections with recordIdsReplicated:false - i.e. recordIds are not caller provided
• Inserting records into collections with recordIdsReplicated:true - i.e. recordIds are caller provided

As a result the function's control flow keeps branching and merging and it's hard to understand. We should break the function up to make it easier to understand.

Note - SERVER-88375 exists to perform a proper cleanup of that code / other code as well. So we may want to defer this ticket until SERVER-88375 is done.