Transactions to store metadata merge info when present

ve.dm.Transaction
* Replace operations are now built directly from the
  linear model and automatically determine what metadata
  replace information they need to include:
** retainMetadata
** replaceMetadata
** insertMetadata

ve.dm.Document
* Metadata array created empty and padded out after data parsing
  as we are no longer using Document.spliceData to build it (a new
  test checks for correct metadata length)
* spliceData replaced with getMetadataReplace, which instead returns
  transactional steps of spliceData (retain, replace, insert)

ve.dm.MetaLinearData
* Add function for merging metadata items together. Only used
  once in the code (Document.getMetadataReplace) but useful
  for generating test data.

ve.dm.MetaList
* Replace operations with metadata need to calculate new offset
  and indices directly, but can't be applied immediately lest they
  put a metaItem out of place and affect findItem.

ve.dm.MetaItem
* Add methods to support queued moves as required by MetaList

Test files
* Updated to match new pushReplace API
* Remove any instances of Document.spliceData
* Extra check on sparse metadata array length
* Rewrite spliceData tests as getMetadataReplace tests
* Count expected cases in Transaction(Processor) tests

Bug: 46954
Change-Id: I4edad1c2dd37c723bff2792bab7d694ef17a86dc
Merge "Transactions to store metadata merge info when present"