Possibly coalesce multiple sequential ExecuteBlocksFromFile into a single ExecuteBlocksFromFile

[bradgrantham-lunarg]

In a recent test of asset file captures I did on vkcube, there were 3 sequential commands written to asset files in a row (InitBufferCommand, InitBufferCommand, InitImageCommand) to asset file as sequential ExecuteBlocksFromFile of 1 block. For larger captures this number may be very large. Investigate lazily writing out a single ExecuteBlocksFromFile if many sequential commands would be written to the asset file without other intervening commands in the main capture file.

@panos-lunarg for awareness