Speed up - investigate not inserting element aspects in a 1-1 element transformation

[MichaelBelousov]

If a transformation does not create or merge multiple elements from or into 1, we can probably just use the preserved federation guid instead of an external source aspect to merge it. We should investigate this, as not creating external source aspects could significantly increase performance

Remaining priority issues:

• [x] #38
• [x] #39
• [x] #40

1.x release list:

• fix validation of transformer resumption it's broken in the original branch and can't be fixed, deferring and will probably deprecate. Should just restart the transformation from the beginning and that should work.
• allow configuring an ChangedInstanceDataProvider which can use e.g. the changed element service to more efficiently run through element changes.
• [x] experiment with reading changesets directly instead of using ECDb Change tables and changecache since that requires applying changesets which is expensive (let's profile first)
• [ ] check all FIXMEs for recommended test coversage
• [ ] update existing iTwin.js documentation about provenance
• [ ] rename new (BranchProvenanceInitializer).initializeBranchProvenance function to be a namespace IModelBranchingOperations.initializeFork
• [ ] delete previously deprecated APIs
• [ ] remove all beta docs tags
• [ ] make targetScopeElement a required argument in the case of a synchronization
• [ ] deprecate wasSourceIModelCopiedToTarget
• [ ] fix transformCallbackFor's second instanceof Element check to be on models

[MichaelBelousov]

initial results showing a potential improvement of ~40% in identity-transform-into-empty when source contains federation guids

[MichaelBelousov]

this can be merged soon, it is basically done and already available on the -fedguidopt release tag