[Web] Refactor TextEditingDelta implementation #105243
Description
The TextEditingDelta implementation on web currently continually updates an editingDeltaState during the process of text-input (beforeInput, onInput, compositionupdate), until we have arrived at a final editingDeltaState. Having it spread across many handlers can make it difficult to make updates to the DefaultTextEditingStrategy without breaking TextEditingDeltas. An example of this is flutter/engine#33590 which adds composing region tracking, but broke TextEditingDeltas at first (later resolved).
Proposal:
Use the lastEditingState and the newEditingState to determine the state of a TextEditingDelta, and centralize the logic into inferDeltaState.